Don't ignore errors raised by `PyErr_WarnFormat` in `warn_about_fork_with_threads`
Instead, ignore the warnings in all test code that forks. (That's a lot of functions.)
In `test_support`, make `ignore_warnings` a context manager (as well as decorator),
and add a `message` argument to it.
Also add a `ignore_fork_in_thread_deprecation_warnings` helper for the deadlock-in-fork
warning.
Make `warnings.catch_warnings()` use a context variable for holding
the warning filtering state if the `sys.flags.context_aware_warnings`
flag is set to true. This makes using the context manager thread-safe in
multi-threaded programs.
Add the `sys.flags.thread_inherit_context` flag. If true, starting a new
thread with `threading.Thread` will use a copy of the context
from the caller of `Thread.start()`.
Both these flags are set to true by default for the free-threaded build
and false for the default build.
Move the Python implementation of warnings.py into _py_warnings.py.
Make _contextvars a builtin module.
Co-authored-by: Kumar Aditya <kumaraditya@python.org>
Fix test_copyreg when numpy is installed: test.pickletester now
saves/restores warnings.filters when importing numpy, to ignore
filters installed by numpy.
Add the save_restore_warnings_filters() function to the
test.support.warnings_helper module.
