GeezerVison

Add a primitive for chr(int). Short ints in the valid range call PyUnicode_FromOrdinal directly, instead of looking up builtins.chr and calling it through vectorcall with a boxed argument.

Out-of-range arguments raise the same exceptions as CPython. These differ between Python versions: 3.13+ always raises ValueError, while 3.12 and earlier raise OverflowError for values that don't fit in a C int.

Tests compare the results against CPython for every code point and for a range of out-of-range values, including ints that don't fit in a short tagged int. They pass on Python 3.10, 3.12, 3.13 and 3.14.

Micro-benchmark (~2M calls, chr(i) for i in range(32, 1024), the same module compiled before and after this change, Python 3.13): 0.065s -> 0.019s.

This covers the chr part of #15937, which has been inactive since 2024. ord(str) has since been added separately.

Part of mypyc/mypyc#644.