gh-128923: Use zero to indicate unassigned unique id

[colesbury]

In the free threading build, the per thread reference counting uses a unique id for some objects to index into the local reference count table. Use 0 instead of -1 to indicate that the id is not assigned. This avoids bugs where zero-initialized heap type objects look like they have a unique id assigned.

• Issue: Reference counting bug with manually allocated heap types #128923

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Android 3.x has failed when building commit d66c08a.

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/1594/builds/1046) and take a look at the build logs.
4. Check if the failure is related to this commit (d66c08a) 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/1594/builds/1046

Failed tests:

• test.test_pydoc.test_pydoc

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/test_pydoc/test_pydoc.py", line 559, in test_builtin_with_more_than_four_children
    text = doc.docclass(object)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/pydoc.py", line 1436, in docclass
    subclasses = sorted(
        (str(cls.__name__) for cls in type.__subclasses__(object)
         if not cls.__name__.startswith("_") and cls.__module__ == "builtins"),
        key=str.lower
    )
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/pydoc.py", line 1438, in <genexpr>
    if not cls.__name__.startswith("_") and cls.__module__ == "builtins"),
                                            ^^^^^^^^^^^^^^
AttributeError: __module__. Did you mean: '__reduce__'?

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot iOS ARM64 Simulator 3.x has failed when building commit d66c08a.

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/2346) and take a look at the build logs.
4. Check if the failure is related to this commit (d66c08a) 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/2346

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

==

Click to see traceback logs

Traceback (most recent call last):

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Android 3.x has failed when building commit d66c08a.

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/1591/builds/937) and take a look at the build logs.
4. Check if the failure is related to this commit (d66c08a) 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/1591/builds/937

Failed tests:

• test.test_pydoc.test_pydoc

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/test/test_pydoc/test_pydoc.py", line 559, in test_builtin_with_more_than_four_children
    text = doc.docclass(object)
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/pydoc.py", line 1436, in docclass
    subclasses = sorted(
        (str(cls.__name__) for cls in type.__subclasses__(object)
         if not cls.__name__.startswith("_") and cls.__module__ == "builtins"),
        key=str.lower
    )
  File "/data/user/0/org.python.testbed/files/python/lib/python3.14/pydoc.py", line 1438, in <genexpr>
    if not cls.__name__.startswith("_") and cls.__module__ == "builtins"),
                                            ^^^^^^^^^^^^^^
AttributeError: __module__. Did you mean: '__reduce__'?

[Yhg1s]

Re: the buildbot failures, they're happening because the newly added heaptype inherits from object and does not have the __module__ attribute. Given that creating classes this way (and them not having __module__) isn't inherently wrong, I think the correct fix is to make pydoc robust against this.

[Yhg1s]

#128951 should fix the buildbot failures. (This wasn't picked up by GHA because we apparently have no GHA that runs the tests in a single process/sequentially.)