This adds:
- Many more exceptions.
- HPyArg_ support for tracking new handles during parsing.
- HPyArg_ support for all number formats.
- New HPyLong_ API functions for converting handles to different C representations.
- New HPyBytes API functions for converting C character strings into bytes handles.
- HPyBytes_FromStringAndSize raises a ValueError if a NULL string is passed to it (the underlying character buffer is not editable via the HPy API anyway, so returning a buffer to uninitialized memory is not particularly useful).
- HPyErr_SetObject for setting exceptions.