Fix warning filter precedence across test scopes

[K-kiron]

With a class-level filterwarnings("error") mark, a parameter marked filterwarnings("ignore") still fails. The class filter is applied after the parameter filter and ends up taking precedence. The same issue affects module-level filters.

I changed warning filtering to apply outer-scope filters first, keeping the existing order within each node. This lets more specific filters override the defaults without changing shared marker iteration or storage.

The regression tests cover conflicting filters across scopes, existing decorator and argument ordering, and parameter-specific overrides. I also documented the precedence and added a changelog entry.

Fixes #10406.

Running python -m pytest testing/test_warnings.py testing/test_mark.py testing/python/metafunc.py -q --tb=short on Windows with Python 3.11.5 gives 338 passed, 4 skipped, and 1 xfailed. Pre-commit also passes for the changed files.

[K-kiron]

The PyPy job fails in TestMetafunc.test_idval_hypothesis while Hypothesis imports numpy.random, with a CYTHON_USE_TYPE_SPECS=1 RuntimeWarning.

I found the same failure in #15086:
https://github.com/pytest-dev/pytest/actions/runs/35784033528/job/106936914376

Both runs use PyPy 8.0.0, while the passing main run used PyPy 7.3.23. This looks like a PyPy/NumPy compatibility issue. The other 29 test matrix jobs passed.