available only when Py_LIMITED_API is set to the PY_VERSION_HEX value of
the minimum Python version supporting this API.

This affects documentation, code comments, and a debugging messages.

This function gives a control to the buffer size without using min_size.

Issue #25401: Optimize bytes.fromhex() and bytearray.fromhex(): they are now
between 2x and 3.5x faster. Changes:

* Use a fast-path working on a char* string for ASCII string
* Use a slow-path for non-ASCII string
* Replace slow hex_digit_to_int() function with a O(1) lookup in
  _PyLong_DigitValue precomputed table
* Use _PyBytesWriter API to handle the buffer
* Add unit tests to check the error position in error messages

Issue #25399: Don't create temporary bytes objects: modify _PyBytes_Format() to
create work directly on bytearray objects.

* Rename _PyBytes_Format() to _PyBytes_FormatEx() just in case if something
  outside CPython uses it
* _PyBytes_FormatEx() now uses (char*, Py_ssize_t) for the input string, so
  bytearray_format() doesn't need tot create a temporary input bytes object
* Add use_bytearray parameter to _PyBytes_FormatEx() which is passed to
  _PyBytesWriter, to create a bytearray buffer instead of a bytes buffer

Most formatting operations are now between 2.5 and 5 times faster.

Issue #25399: Add a new use_bytearray attribute to _PyBytesWriter to use a
bytearray buffer, instead of using a bytes object.