ThreadingMock.call_count is not thread-safe (race condition) #150175

Bug Description

ThreadingMock._increment_mock_call() is not thread-safe.
Multiple threads calling the mock simultaneously lose increments
due to race conditions on call_count and other attributes.

Reproducer

import threading
import unittest.mock

m = unittest.mock.ThreadingMock()
LOOPS = 10000
THREADS = 50

def test_function():
    for _ in range(LOOPS):
        m()

threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
for t in threads:
    t.start()
for t in threads:
    t.join()

assert m.call_count == LOOPS * THREADS  # FAILS intermittently!

Expected vs Actual

• Expected: 500000
• Got: ~460000 (missing calls lost to race condition)

Environment

• Python 3.14
• Reproducible on ARM64 and x86 under load
• Reported via Yocto Project: https://bugzilla.yoctoproject.org/show_bug.cgi?id=16213

Linked PRs

• gh-150175: Fix ThreadingMock call_count race condition #150176
• [3.13] gh-150175: Fix ThreadingMock call_count race condition (GH-150176) #150180
• [3.14] gh-150175: Fix ThreadingMock call_count race condition (GH-150176) #150181
• [3.15] gh-150175: Fix ThreadingMock call_count race condition (GH-150176) #150182