gh-154014: Initialize cold executor vm_data fields

[BHUVANSH855]

Issue

Fixes gh-154014.

Summary

make_cold_executor() allocates cold executors directly via
allocate_executor() and bypasses _Py_ExecutorInit(). As a result,
vm_data.valid and vm_data.pending_deletion remain uninitialized.

During interpreter shutdown, interpreter_clear() asserts that
cold->vm_data.valid is true, causing assertion failures when CPython is
built with --enable-experimental-jit --with-assertions.

This change initializes the required vm_data fields for cold executors,
restoring the expected invariant during shutdown.

Testing

Reproduced the original crash reported in the issue using:

./configure --enable-experimental-jit --with-assertions
make -j$(nproc)

Before this change, _bootstrap_python aborted with:

Assertion `cold->vm_data.valid' failed.

After this change:

• make -j$(nproc) completes successfully.
• The full CPython regression test suite passes.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[Fidget-Spinner]

Looks good, just needs style cleanups.

[Fidget-Spinner]

Please add a news entry as well, and a test reproducer in Lib/test/test_capi/test_opt.py.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[BHUVANSH855]

Thanks for the review @Fidget-Spinner

I've addressed the requested changes:

• removed the stray formatting changes,
• added a NEWS entry,
• added a regression test in Lib/test/test_capi/test_opt.py.

The CI is now running on the updated branch. I'd appreciate another look when you have a chance. Thanks!

[cocolato]

we can release unregistered cold executors directly

[cocolato]

Thanks! let's wait for Ken Jin's review :)