I modified the json module to replace the private _PyUnicodeWriter C API with the public PyUnicodeWriter C API:

• 6e63c47
• c914212

Problem: it made the json module slower. Let's investigate what's going on.

Linked PRs

• gh-133968: Use private unicode writer for json #133832
• gh-133968: Add fast path to PyUnicodeWriter_WriteStr() #133969
• [3.14] gh-133968: Add fast path to PyUnicodeWriter_WriteStr() (GH-133969) #133971
• gh-133968: Add PyUnicodeWriter_WriteASCII() function #133973
• [3.14] gh-133968: Add PyUnicodeWriter_WriteASCII() function (#133973) #134974
• gh-133968: Update PyUnicodeWriter_WriteASCII() documentation #135297