feat(references): add ticket reference footers

Refs: #4

tests/error_tests.rs

@@ -170,7 +170,7 @@ fn test_from_poison_error() {
 /// Test from_revset_evaluation_error constructs RevsetResolutionError
 #[test]
 fn test_from_revset_evaluation_error() {
-    let underlying = std::io::Error::new(std::io::ErrorKind::Other, "store failure");
+    let underlying = std::io::Error::other("store failure");
     let eval_err = jj_lib::revset::RevsetEvaluationError::Other(Box::new(underlying));
     let error = Error::from_revset_evaluation_error("@", eval_err);
     assert!(matches!(error, Error::RevsetResolutionError { .. }));
@@ -281,7 +281,7 @@ fn test_error_matching_all_variants() {
     }
 
     // Verify all variants can be cloned
-    let cloned: Vec<Error> = variants.iter().map(|e| e.clone()).collect();
+    let cloned: Vec<Error> = variants.to_vec();
     assert_eq!(variants.len(), cloned.len());
     for (original, clone) in variants.iter().zip(cloned.iter()) {
         assert_eq!(original, clone);