Apply and enforce ruff rules (RUF)

Apply ruff rule RUF012:
RUF012 Mutable class attributes should be annotated with `typing.ClassVar`

Disable ruff rule RUF001

Author: DimitriPapadopoulos

numcodecs/ndarray_like.py

@@ -1,4 +1,4 @@
-from typing import Any, Dict, Optional, Protocol, Tuple, Type, runtime_checkable
+from typing import Any, ClassVar, Dict, Optional, Protocol, Tuple, Type, runtime_checkable
 
 
 class _CachedProtocolMeta(Protocol.__class__):
@@ -11,7 +11,7 @@ class _CachedProtocolMeta(Protocol.__class__):
     isinstance checks using the object's class as the cache key.
     """
 
-    _instancecheck_cache: Dict[Tuple[Type, Type], bool] = {}
+    _instancecheck_cache: ClassVar[Dict[Tuple[Type, Type], bool]] = {}
 
     def __instancecheck__(self, instance):
         key = (self, instance.__class__)

pyproject.toml

@@ -133,5 +133,9 @@ environment = { DISABLE_NUMCODECS_AVX2=1, DISABLE_NUMCODECS_SSE2=1 }
 [tool.ruff]
 line-length = 100
 
+[tool.ruff.lint]
+extend-select = [ "RUF" ]
+ignore = [ "RUF001" ]
+
 [tool.ruff.format]
 quote-style = "preserve"