fix(extract): emit inherits edge for Python parameterized bases

[Synvoya]

Bug

Python parameterized bases were dropped. class Repo(Base[int]) emitted no inherits edge even though class Repo(Base) worked.

Root cause

The Python heritage walker accepted only identifier nodes. A parameterized base parses as subscript, with the concrete base in its value field and type arguments inside the brackets.

Fix

For a subscript heritage entry, unwrap its value before applying the existing identifier-only rule. Bare bases are unchanged.

The scope is intentionally narrow: qualified attribute bases and runtime expressions are separate resolution problems. They remain skipped instead of creating a potentially incorrect local target.

Validation

• Covers single and mixed parameterized bases.
• Covers nested type arguments such as Base[list[str]].
• Retains bare-identifier inheritance.
• Verifies generic arguments do not become parent edges.
• Verifies a runtime base factory does not fabricate an inheritance edge.
• tests/test_languages.py: 319 passed, 13 optional-DM skips.
• Ruff and git diff --check: passed.