winreg_QueryValueEx_impl doesn't use retSize

[youknowone]

Bug report

Bug description:

The actual data size in buffer is not bufSize, but retSize.

https://github.com/python/cpython/blob/v3.14.1/PC/winreg.c#L1657-L1684

This is not causing an actual bug because Reg2Py is additionally checking the null-terminated string length.
I could cause actual bug: https://github.com/python/cpython/pull/142283/files#r2591736333

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-142282 Fix winreg_QueryValueEx_impl to use retSize #142283