gh-136681: make argsbuf static to speedup processing positional arguments with AC

[skirpichev]

• Issue: Slow functions calls for C-coded functions, accepting positional-or-kwarg argument vs positional-only #136681

[skirpichev]

benchmark: #136681 (comment)

[ZeroIntensity]

Won't this break when called concurrently?

[skirpichev]

Won't this break when called concurrently?

Yes, apparently it does :-( Probably, this can't be fixed easily.

Alternative approach should work: #136681 (comment). The _PyArg_UnpackKeywords() is implemented as a macro (which encodes fast-path) and a function. So, the if condition should keep negation of the fast-path condition in the macro (which can be removed).