UBsan: Remove _Py_NO_SANITIZE_UNDEFINED

[encukou]

Bug report

Split out from the #111178 monster-issue:

We use the macro _Py_NO_SANITIZE_UNDEFINED to disable the UB sanitizer in some hard-to-fix cases, so that we can get a stable, regression-monitoring checker sooner.
To fully fix UBsan failures, we should get rid of the macro.
At least outside test functions.

Linked PRs

• gh-133157: remove use of _Py_NO_SANITIZE_UNDEFINED in faulthandler #134047
• gh-133157: remove usage of _Py_NO_SANITIZE_UNDEFINED in Parser/pegen.c #134048
• gh-133157: remove usage of _Py_NO_SANITIZE_UNDEFINED in pyexpat #134050