Stabilize the test suite

[mcepl]

This PR stabilizes pook's patching mechanisms for modern runtimes (Python 3.13+) and newer third-party package APIs:

• Robust mock.patch helper (resolve_path): Replaced calls to the undocumented/internal patcher.get_original() method with a robust dynamic resolver (resolve_path). This safely resolves original, unpatched target objects before unittest.mock.patch wraps them.
• Graceful Optional Dependencies: All resolving and patching are safely wrapped inside try...except Exception: pass blocks, preserving pook's clean fallback behavior in environments where optional clients (like httpx or urllib3) are not installed.
• Fixed aiohttp compatibility: Added dynamic signature inspection to session._response_class.__init__ to gracefully supply a mock stream_writer argument. This directly resolves TypeError: ClientResponse.__init__() missing 1 required keyword-only argument: 'stream_writer' failures on newer aiohttp >= 3.9 releases.
• Refactored headers.py assertions: Converted fragile assert statements into explicit if not ...: raise AssertionError(...) blocks, ensuring validation logic is consistently executed and not stripped out under Python's optimized mode (-O).

Recent changes to internal Python mocking details and third-party package APIs (like aiohttp) broke pook's interceptors. This patch resolves these issues cleanly and ensures full compatibility without introducing hard dependency requirements on optional HTTP clients.

PR Checklist

• I've added tests for any code changes (this is all about fixing the test suite, so not completely relevant)
• I've documented any new features (there are no new futures)