test(try-repo): add integration tests for builtin and meta repos

Add comprehensive tests for try-repo with builtin and meta hook repos:
- Basic hook execution (trailing-whitespace, identity)
- Multiple hooks and all-hooks invocation
- Hook filtering with --skip
- Invalid hook ID error handling
- Case-insensitive repo name matching
- Config warning, meta skip, check-hooks-apply, check-useless-excludes

Extract test helpers: init_git_repo, setup_basic_context, and
filters_with_sha to reduce duplication across test cases.

Author: shaanmajid