Ensure init called in protocol subclasses

[JanEricNitschke]

Discovered through CPython 3.12 test_typing.py: https://github.com/JanEricNitschke/typing_extensions/actions/runs/17639167194/job/50121940225#step:7:36

Tests are from here:

• bpo-44806: Fix __init__ in subclasses of protocols cpython#27545
• bpo-45081: Fix __init__ method generation when inheriting from Protocol cpython#28121
• bpo-45081: Fix __init__ method generation when inheriting from Protocol cpython#28121

Code is from current CPython:

• https://github.com/python/cpython/blob/main/Lib/typing.py#L1843
• https://github.com/python/cpython/blob/main/Lib/typing.py#L2121

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (364c9e0) to head (0daa685).
⚠️ Report is 27 commits behind head on main.

@@ Coverage Diff @@## main #678 +/- ##
=======================================
Coverage 97.39% 97.40% =======================================
Files 3 3 Lines 7767 7793 +26 =======================================
+ Hits 7565 7591 +26 
Misses 202 202 

Flag	Coverage Δ
3.10	89.11% <100.00%> (+0.03%)	⬆️
3.10.4	89.11% <100.00%> (+0.03%)	⬆️
3.11	88.36% <100.00%> (+0.03%)	⬆️
3.11.0	87.60% <100.00%> (+0.04%)	⬆️
3.12	88.30% <100.00%> (+0.03%)	⬆️
3.12.0	88.29% <100.00%> (+0.03%)	⬆️
3.13	81.93% <96.66%> (+0.09%)	⬆️
3.13.0	82.64% <96.66%> (+0.09%)	⬆️
3.14	78.38% <96.29%> (+0.10%)	⬆️
3.9	89.82% <100.00%> (+0.03%)	⬆️
3.9.12	89.82% <100.00%> (+0.03%)	⬆️
pypy3.10	88.95% <100.00%> (+0.03%)	⬆️
pypy3.11	88.22% <100.00%> (+0.03%)	⬆️
pypy3.9	89.65% <100.00%> (+0.03%)	⬆️

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Files with missing lines	Coverage Δ
src/test_typing_extensions.py	98.41% <100.00%> (+<0.01%)	⬆️
src/typing_extensions.py	93.97% <100.00%> (-0.02%)	⬇️

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[JanEricNitschke]

Anything i can/should still do here? Conflict is only in the changelog.