lib.Types: Restrict LoadTypes to ABC-derived classes

The previous commit reads __abstractmethods__ via a getattr() with an empty
frozenset fallback, because in mypy 2.3.1 the scanned classes are typed as
type[object], which does not declare the attribute.

Add is_abc_class() as a TypeGuard, and skip the classes it rejects with a
debug line: LoadTypes now yields only ABC-derived classes. The guard
narrows to the classes that carry the attribute, so that the debug line can
now read __abstractmethods__ directly.

The command loaders are unaffected: every class they load is derived from
AbstractCmd, and hence from ABC. For loads that rely on the name filter
alone, plain classes are now skipped instead of being yielded.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/Types.py

@@ -5,7 +5,7 @@ import os
 import re
 import sys
 
-from typing import TYPE_CHECKING, Any, Generic, Iterable, TypeVar, override
+from typing import TYPE_CHECKING, Any, Generic, Iterable, TypeGuard, TypeVar, override
 
 from .log import ERR, OFF, log, parse_log_level
 
@@ -15,6 +15,9 @@ if TYPE_CHECKING:
 
 T = TypeVar('T')
 
+def is_abc_class(c: type[object]) -> TypeGuard[abc.ABCMeta]:
+    return isinstance(c, abc.ABCMeta)
+
 class Types(abc.ABC, Iterable[type[T]], Generic[T]):  # export
 
     @override
@@ -101,11 +104,11 @@ class LoadTypes(Types[T]):  # export
                     if rx is not None and not re.match(rx, member_name):
                         self._debug(f'o "{name}" has wrong name')
                         continue
+                    if not is_abc_class(c):
+                        self._debug(f'o "{name}" is not derived from ABCMeta')
+                        continue
                     if inspect.isabstract(c):
-                        abstract: frozenset[str] = getattr(
-                            c, '__abstractmethods__', frozenset()
-                        )
-                        self._debug(f'o "{name}" is abstract: {abstract}')
+                        self._debug(f'o "{name}" is abstract: {c.__abstractmethods__}')
                         continue
                     if self.__type_filter:
                         for tp in self.__type_filter: