gh-131238: Use pycore_interp_structs.h header

[vstinner]

Replace pycore_runtime_structs.h include with pycore_interp_structs.h include in internal headers.

• Issue: Our internal headers are far too interlinked #131238

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot iOS ARM64 Simulator 3.x (tier-3) has failed when building commit a741102.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1380/builds/2955) and take a look at the build logs.
4. Check if the failure is related to this commit (a741102) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1380/builds/2955

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/4F6EA510-4EA0-4706-8B1F-020FE958C08F/data/Containers/Bundle/Application/DBFDCCFF-85B7-4B66-9B7D-D1A7666166D0/iOSTestbed.app/python/lib/python3.14/threading.py", line 1054, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/Users/buildbot/Library/Developer/XCTestDevices/4F6EA510-4EA0-4706-8B1F-020FE958C08F/data/Containers/Bundle/Application/DBFDCCFF-85B7-4B66-9B7D-D1A7666166D0/iOSTestbed.app/python/lib/python3.14/threading.py", line 996, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/Library/Developer/XCTestDevices/4F6EA510-4EA0-4706-8B1F-020FE958C08F/data/Containers/Bundle/Application/DBFDCCFF-85B7-4B66-9B7D-D1A7666166D0/iOSTestbed.app/python/lib/python3.14/test/test_interpreters/test_stress.py", line 47, in run
    interp = interpreters.create()
  File "/Users/buildbot/Library/Developer/XCTestDevices/4F6EA510-4EA0-4706-8B1F-020FE958C08F/data/Containers/Bundle/Application/DBFDCCFF-85B7-4B66-9B7D-D1A7666166D0/iOSTestbed.app/python/lib/python3.14/test/support/interpreters/__init__.py", line 76, in create
    id = _interpreters.create(reqrefs=True)
interpreters.InterpreterError: interpreter creation failed
k

[freakboy3742]

The iOS failure is an intermittent issue that I've seen a couple of times - it passes on a re-run in the test, and almost always passes cleanly. It's unrelated to this PR; I've logged the underlying problem as #131485.