b05775b581
- Rename _BACKENDS → _backends: pyright treats uppercase module-level names as constants and flags the reassignment in _get_backends() as reportConstantRedefinition; lowercase avoids this. - Add TYPE_CHECKING guard importing CommitCancelled/Freezer/get_freezer from .freeze: pyright cannot see module-level __getattr__ bindings, so reportUnsupportedDunderAll fired for those three __all__ entries; the guard makes them visible to the type checker without running at import time. - Update test_backend_selection.py to patch _backends (lowercase).