feat(gix): resolve revisions and repository metadata natively

Handle verified revisions and repository metadata exposed by GixPython.
Keep Git's initial repository validation and unsupported discovery options.
Message searches, dirty suffixes and describe-shaped names fall back because
the native grammar differs in regex handling and exact-tag precedence
(`GIX-14`/`GIX-17`).

Keep `rev-parse --show-ref-format` on the CLI: GixPython 0.1.0 exposes no
repository reference-storage-format getter (`GIX-1`). Rejecting reftable
elsewhere is not a native query, so do not fabricate a `files` answer.
This restores one CLI invocation per such query (previously zero after
wrapper initialization); the fallback regression checks this explicitly.

Validation: focused backend and revision tests passed with Gix first
(26 passed in 18.67s), then CLI (22 passed, 1 skipped in 19.54s).
Ruff lint/format and `git diff --check` passed.

Author: codex

git/_backend.py

@@ -124,7 +124,27 @@ def object_data(command: Any, ref: bytes, *, stream: bool = False) -> Any:
     return result
 
 
-_HANDLERS: Dict[str, Callable[[Any, List[str], Dict[str, Any]], bytes]] = {}
+def _rev_parse(repo: Any, args: List[str], kwargs: Dict[str, Any]) -> bytes:
+    if args == ["--path-format=absolute", "--git-common-dir"]:
+        return os.fsencode(os.path.abspath(repo.common_dir())) + b"\n"
+    if args == ["--is-bare-repository"]:
+        return b"true\n" if repo.is_bare() else b"false\n"
+    if args == ["--show-object-format"]:
+        return str(repo.object_hash()).encode("ascii") + b"\n"
+    if args == ["--show-ref-format"]:
+        raise _Unsupported("reference storage format query (GIX-1)")
+    if args == ["--show-toplevel"] and repo.workdir() is not None:
+        return os.fsencode(os.path.abspath(repo.workdir())) + b"\n"
+    if args[:1] != ["--verify"] or args[-2:-1] != ["--end-of-options"]:
+        raise _Unsupported("discovery or revision options")
+    if args[:-2] not in (["--verify"], ["--verify", "--quiet"]):
+        raise _Unsupported("revision options")
+    return str(_oid(repo, args[-1])).encode("ascii") + b"\n"
+
+
+_HANDLERS: Dict[str, Callable[[Any, List[str], Dict[str, Any]], bytes]] = {
+    "rev_parse": _rev_parse,
+}
 
 
 def dispatch(

test/test_gix_backend.py

@@ -30,7 +30,8 @@ def test_unknown_command_and_storage_environment_use_cli(repo):
         assert repo.git._call_process_safe("for_each_ref", "--format=%(refname)", "--", "refs/*") == "fallback"
         with repo.git.custom_environment(GIT_INDEX_FILE=".git/index"):
             assert repo.git._call_process_safe("ls_files", "--stage", "-v", "-z", "--full-name") == "fallback"
-        assert cli.call_count == 2
+        assert repo.git._call_process_safe("rev_parse", "--show-ref-format") == "fallback"
+        assert cli.call_count == 3
 
 
 def test_partial_native_stream_does_not_corrupt_next_read(repo):