gh-157838: Merge biased refcounts on behalf of detached threads

[kumaraditya303]

• Issue: Memory held for too long by the BRC queue while the owning thread is detached #157838

[colesbury]

LGTM

I think this deserves a NEWS entry. A test would also be good

[miss-islington-app]

Thanks @kumaraditya303 for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @kumaraditya303, I could not cleanly backport this to 3.15 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 030e913a742cef279c34349a3d3899feef07c73e 3.15

[miss-islington-app]

Sorry, @kumaraditya303, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 030e913a742cef279c34349a3d3899feef07c73e 3.14

[bedevere-app]

GH-158011 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-158012 is a backport of this pull request to the 3.14 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows PGO NoGIL Tailcall 3.15 (tier-1) has failed when building commit e538c26.

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/2293/builds/76) and take a look at the build logs.
4. Check if the failure is related to this commit (e538c26) 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/2293/builds/76

Failed tests:

• test_external_inspection

Failed subtests:

• test_tlbc_cache_refresh_after_slot_fill - test.test_external_inspection.TestGetStackTrace.test_tlbc_cache_refresh_after_slot_fill

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "<string>", line 40, in <module>
    cached = lines(u, 2)
  File "<string>", line 18, in lines
    traces = u.get_stack_trace()
OSError: ReadProcessMemory failed for PID 14256 at address 0x1 (size 80, partial read 0 bytes): Windows error 299


Traceback (most recent call last):
  File "C:\bbarea\3.15.itamaro-win64-srv-22-aws.nogil.tailcall.pgo\build\Lib\test\test_external_inspection.py", line 2372, in test_tlbc_cache_refresh_after_slot_fill
    self.assertEqual(
    ~~~~~~~~~~~~~~~~^
        result.returncode, 0,
        ^^^^^^^^^^^^^^^^^^^^^
        f"stdout: {result.stdout}\nstderr: {result.stderr}",
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
AssertionError: 1 != 0 : stdout: 
stderr: OSError: [WinError 299] Only part of a ReadProcessMemory or WriteProcessMemory request was completed


Traceback (most recent call last):
  File "<string>", line 40, in <module>
    cached = lines(u, 2)
  File "<string>", line 18, in lines
    traces = u.get_stack_trace()
OSError: ReadProcessMemory failed for PID 10912 at address 0x1 (size 80, partial read 0 bytes): Windows error 299