feat: add SQLite support behind a sqlite Cargo feature

Adds a SqliteDialect alongside PostgresDialect, gated by mutually exclusive
postgres (default) / sqlite Cargo features, plus a feature-selected
ActiveDatabase type alias used throughout the public Georm/Defaultable
traits. Basic CRUD and Defaultable are fully covered by a new SQLite test
suite (tests/sqlite/*) running against a real SQLite database, alongside
split migrations/sqlite/*.

Two real dialect differences surfaced beyond placeholder syntax:
- SQLite's INTEGER columns type-infer as i64 in sqlx's compile-time query
  macros (unlike Postgres SERIAL -> i32), so the SQLite test models use i64
  for integer PK/FK fields.
- sqlx's SQLite query macros need bind arguments bound to a place rather
  than passed as an inline expression (fixed once, centrally, in
  SqlDialect::generate_relation_lookup).

Composite-key entities with chrono::DateTime columns (tests/composite_key.rs)
are not yet ported to SQLite: SQLite has no TIMESTAMPTZ equivalent, so sqlx
infers TEXT date/time columns as String rather than DateTime<Utc> unless the
query explicitly overrides the column type. That needs per-field type
overrides threaded through the generated queries, left as follow-up.

CI now matrixes over both backends; formatting/audit only run once since
they don't vary by backend. examples/postgres/* stays out of
--no-default-features builds by scoping sqlite lint/test just recipes to
`-p georm` (it depends on georm's default postgres feature via Cargo
feature unification, so building it under --features sqlite at the
workspace level double-activates both dialects).

tests/sqlite/simple_struct.rs

@@ -0,0 +1,159 @@
+#![cfg(feature = "sqlite")]
+
+use georm::Georm;
+use rand::seq::SliceRandom;
+
+use models::Author;
+mod models;
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn find_all_query_works(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let result = Author::find_all(&pool).await?;
+    assert_eq!(3, result.len());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite")]
+async fn find_all_returns_empty_vec_on_empty_table(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let result = Author::find_all(&pool).await?;
+    assert_eq!(0, result.len());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn find_query_works(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let id = 1;
+    let res = Author::find(&pool, &id).await?;
+    assert!(res.is_some());
+    let res = res.unwrap();
+    assert_eq!(String::from("J.R.R. Tolkien"), res.name);
+    assert_eq!(1, res.id);
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite")]
+async fn find_returns_none_if_not_found(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let res = Author::find(&pool, &420).await?;
+    assert!(res.is_none());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite")]
+async fn create_works(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let author = Author {
+        id: 1,
+        name: "J.R.R. Tolkien".into(),
+        ..Default::default()
+    };
+    author.create(&pool).await?;
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(1, all_authors.len());
+    assert_eq!(vec![author], all_authors);
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn create_fails_if_already_exists(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let author = Author {
+        id: 2,
+        name: "Miura Kentaro".into(),
+        ..Default::default()
+    };
+    let result = author.create(&pool).await;
+    assert!(result.is_err());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn update_works(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let expected_initial = Author {
+        name: "J.R.R. Tolkien".into(),
+        id: 1,
+        biography_id: Some(2),
+    };
+    let expected_final = Author {
+        name: "Jolkien Rolkien Rolkien Tolkien".into(),
+        id: 1,
+        biography_id: Some(2),
+    };
+    let tolkien = Author::find(&pool, &1).await?;
+    assert!(tolkien.is_some());
+    let mut tolkien = tolkien.unwrap();
+    assert_eq!(expected_initial, tolkien);
+    tolkien.name = expected_final.name.clone();
+    let updated = tolkien.update(&pool).await?;
+    assert_eq!(expected_final, updated);
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite")]
+async fn update_fails_if_not_already_exists(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let author = Author {
+        id: 2,
+        name: "Miura Kentaro".into(),
+        ..Default::default()
+    };
+    let result = author.update(&pool).await;
+    assert!(result.is_err());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite")]
+async fn should_create_if_does_not_exist(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(0, all_authors.len());
+    let author = Author {
+        id: 4,
+        name: "Miura Kentaro".into(),
+        ..Default::default()
+    };
+    author.upsert(&pool).await?;
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(1, all_authors.len());
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn should_update_if_exist(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(3, all_authors.len());
+    let author = Author {
+        id: 2,
+        name: "Miura Kentaro".into(),
+        ..Default::default()
+    };
+    author.upsert(&pool).await?;
+    let mut all_authors = Author::find_all(&pool).await?;
+    all_authors.sort();
+    assert_eq!(3, all_authors.len());
+    assert_eq!(author, all_authors[1]);
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn delete_by_id_should_delete_only_one_entry(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let id = 2;
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(3, all_authors.len());
+    assert!(all_authors.iter().any(|author| author.get_id() == id));
+    let result = Author::delete_by_id(&pool, &id).await?;
+    assert_eq!(1, result);
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(2, all_authors.len());
+    assert!(all_authors.iter().all(|author| author.get_id() != id));
+    Ok(())
+}
+
+#[sqlx::test(migrations = "./migrations/sqlite", fixtures("simple_struct"))]
+async fn delete_should_delete_current_entity_from_db(pool: sqlx::SqlitePool) -> sqlx::Result<()> {
+    let mut all_authors = Author::find_all(&pool).await?;
+    assert_eq!(3, all_authors.len());
+    all_authors.shuffle(&mut rand::rng());
+    let author = all_authors.first().unwrap();
+    let result = author.delete(&pool).await?;
+    assert_eq!(1, result);
+    let all_authors = Author::find_all(&pool).await?;
+    assert_eq!(2, all_authors.len());
+    assert!(all_authors.iter().all(|a| a.get_id() != author.get_id()));
+    Ok(())
+}