* fix: simplify register_task completion handling
Remove duplicated cancellation logging in Context.register_task while keeping Future inputs compatible with asyncio.create_task semantics. Add regression coverage for coroutine, Future, cancellation, and failure paths.
* fix: prioritize local src in tests_v4
Ensure tests_v4 always imports the working tree package by moving src to sys.path[0] even when another checkout or installed copy is already present.
- Deleted `test_testing_module.py` as it is no longer needed.
- Removed `test_top_level_modules.py` which had no content.
- Eliminated `test_transport.py` due to redundancy.
- Cleared out `test_wire_codecs.py` as part of the cleanup.
