Move call target normalization into C tracer

[nyashahama]

Addresses part of #115.

This moves the call target normalization currently done inside TracingModule.trace_op() into the existing _crosshair_tracers C extension. The stack decoding remains in call_stack_info() from #410, while keyword normalization and replacement write-back stay in Python, so this keeps the behavior boundary small.

What changed:

• Added _crosshair_tracers.normalize_call_target() for the __self__ / __call__ / __func__ / type-level descriptor normalization path.
• Updated TracingModule.trace_op() to call the C helper before handling keyword dictionaries and trace_call().
• Added direct tests for bound Python methods, callable instances, C-level bound methods, reference stability, and non-AttributeError propagation during type-level lookup.
• Added an integration test showing callable instance calls still get patched through the tracer.

This includes the error handling requested on #411: type-level lookup clears AttributeError, but propagates other descriptor/access errors instead of continuing with an exception set.

This intentionally does not touch the open CompositeTracer removal work in #409 or the opcode callback argument caching work in #412.

Verification:

• python3 -m venv .venv && .venv/bin/python -m pip install --upgrade pip setuptools wheel && .venv/bin/python -m pip install --editable '.[dev]'
• .venv/bin/python setup.py build_ext --inplace
• PYTHONHASHSEED=0 .venv/bin/python -m pytest crosshair/tracers_test.py::test_normalize_call_target_helper_is_exported -q failed before implementation as expected.
• PYTHONHASHSEED=0 .venv/bin/python -m pytest crosshair/tracers_test.py crosshair/_tracers_test.py -q -> 18 passed
• PYTHONHASHSEED=0 .venv/bin/python -m pytest crosshair/core_test.py crosshair/libimpl/builtinslib_test.py crosshair/tracers_test.py crosshair/_tracers_test.py -q -> 564 passed, 2 skipped
• CROSSHAIR_EXTRA_ASSERTS=1 PYTHONHASHSEED=0 .venv/bin/python -m pytest crosshair/core_test.py crosshair/libimpl/builtinslib_test.py crosshair/tracers_test.py crosshair/_tracers_test.py -q -> 564 passed, 2 skipped
• CROSSHAIR_EXTRA_ASSERTS=1 PYTHONHASHSEED=0 .venv/bin/python -m pytest -m smoke -n auto --dist worksteal crosshair -q -> 13 passed
• .venv/bin/python -m black --check crosshair/tracers.py crosshair/tracers_test.py
• .venv/bin/python -m isort --check-only crosshair/tracers.py crosshair/tracers_test.py
• .venv/bin/pre-commit run flake8 --files crosshair/tracers.py crosshair/tracers_test.py
• git diff --check

I also attempted the full local xdist suite. It reported 8 failures in symbolic/time-sensitive areas under local parallel load; each failed nodeid that I reran in isolation passed with PYTHONHASHSEED=0. I left this note here so CI remains the source of truth for the full matrix.

[pschanely]

Thank you!