_HOOK_ORDER was a flat list of hook names with no way to express which hooks can safely run in parallel (relevant for prek priority groups). Replace it with a HOOK_GROUPS: list[list[str]] where each inner list is a group of hooks at the same priority level.

Structure

HOOK_GROUPS: list[list[str]] = [
    ["sync-with-uv", "validate-pyproject", "uv-export", "pyproject-fmt", "ruff", "ruff-check"],
    ["ruff-format"],
    ["ty", "deptry", "lint_imports", "import-linter", "tach", "codespell"],
]

• Group 0: Setup, validation, formatting, lint+fix
• Group 1: Code formatting (depends on group 0, e.g. ruff-format after ruff-check)
• Group 2: Read-only checkers (safe to run in parallel)

Flattening produces the same ordering as the original _HOOK_ORDER.

Changes

• hooks.py: Replace _HOOK_ORDER with HOOK_GROUPS, flatten inline in add_repo() for index-based ordering
• test_core_tool.py: Update import and flatten before membership check
• test_hooks.py: Add TestHookGroups (structure validation, no duplicates, non-empty), update comments