feat(cli): add jj-lib version to version output

build.rs

@@ -0,0 +1,13 @@
+use cargo_lock::Lockfile;
+
+fn main() {
+    let lockfile = Lockfile::load("Cargo.lock").expect("Cargo.lock not found");
+    let version = lockfile
+        .packages
+        .iter()
+        .find(|p| p.name.as_str() == "jj-lib")
+        .map(|p| p.version.to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+    println!("cargo:rustc-env=JJ_LIB_VERSION={version}");
+    println!("cargo:rerun-if-changed=Cargo.lock");
+}