Improve pure Python rev-parse coverage and behavior

[Copilot]

Port object-resolving revspec cases inspired by gix-revision into deterministic GitPython tests, without shelling out to Git or Gix at runtime. Refactor rev_parse handling around anchors, navigation, peeling, reflog selectors, path/index lookups, describe-style names, and commit-message searches.

Document observed Git/Gix behavior differences and the GitPython choices made for user-facing compatibility.

[Copilot]

Pull request overview

This PR addresses issue #2135 by updating GitPython’s revision parsing so Repo.commit()/rev_parse() can resolve tag names that start with @ (e.g., @foo) without misinterpreting them as reflog syntax.

Changes:

• Add regression tests for repo.commit("@foo") and for rev_parse() handling of names beginning with @.
• Refactor and extend rev_parse() parsing logic to better distinguish tokens vs. literal @ in ref names, and to support additional rev-parse forms.
• Add helper functions for reflog parsing, message search, and describe-style name resolution.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
git/repo/fun.py	Refactors rev_parse() tokenization and adds helpers for reflog/message-search/describe parsing to prevent @-prefixed tags from failing.
test/test_repo.py	Adds a regression test covering Repo.commit() with a tag name starting with @.
test/test_rev_parse.py	Introduces a new pytest module covering rev_parse() behavior for @ names, navigation/peeling, reflog selectors, and invalid specs.

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[Copilot]

Pull request overview

Adds expanded revision-spec parsing behavior and a dedicated test suite to increase deterministic coverage of Repo.rev_parse edge cases (describe-style names, navigation/peeling, reflog selectors, index/tree path lookups, and commit-message searches).

Changes:

• Introduce a new test/test_rev_parse.py with targeted revspec cases and a purpose-built repo fixture.
• Extend git/repo/fun.py::rev_parse and helpers to support additional revspec forms (describe-style names, reflog selectors, path/index lookups, and message searches).
• Add/adjust tests in test/test_repo.py for tags starting with @ and make reflog-history assertions more robust.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/test_rev_parse.py	New focused rev-parse test suite and fixture repo construction.
test/test_repo.py	Adds regression coverage for @foo tags and stabilizes a reflog assertion.
git/repo/fun.py	Refactors/enhances rev_parse with new parsing helpers and added revspec support.

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