array.array: Remove tostring() and fromstring() methods.  They were
aliases to tobytes() and frombytes(), deprecated since Python 3.2.

The `arraymodule`'s `b_getitem` function returns a `PyLong` converted 
from `arrayobject`'s array, by dereferencing a pointer to `char`.

When the `char` type is `signed char`, the `if (x >= 128) x -= 256;` comparison/code is redundant because a `signed char` will have a value of `[-128, 127]` and so `x` will never be greater or equal than 128.

This check was indeed needed for situations where a given compiler would assume `char` being `unsigned char` which would make `x` in `[0, 256]` range.

However, the check can be removed if we cast the `ob_item` into a signed char pointer (`signed char*`) instead of `char*`.

This PR/commit introduces this change.

Automatically replace
tp_print -> tp_vectorcall_offset
tp_compare -> tp_as_async
tp_reserved -> tp_as_async

Adds sys.audit, sys.addaudithook, io.open_code, and associated C APIs.

The final addition (cur += step) may overflow, so use size_t for "cur".
"cur" is always positive (even for negative steps), so it is safe to use
size_t here.

Co-Authored-By: Martin Panter <vadmium+py@gmail.com>

Deprecate using the __int__() method in implicit conversions of Python
numbers to C integers.