fix(exports): add Enableable to package exports

Fix ImportError by exporting Enableable, is_enableable, mark_enableable,
and ENABLED_FIELD from the enableable module in __init__.py.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: trissim

src/python_introspect/__init__.py

@@ -30,6 +30,12 @@
     DocstringParsingError,
     TypeResolutionError,
 )
+from .enableable import (
+    Enableable,
+    is_enableable,
+    mark_enableable,
+    ENABLED_FIELD,
+)
 
 __all__ = [
     # Version
@@ -50,4 +56,9 @@
     "SignatureAnalysisError",
     "DocstringParsingError",
     "TypeResolutionError",
+    # Enableable
+    "Enableable",
+    "is_enableable",
+    "mark_enableable",
+    "ENABLED_FIELD",
 ]