gh-89653: PEP 670: Convert PyBytes macros to functions (#91990)

Convert the following macros to static inline functions:

* PyByteArray_AS_STRING()
* PyByteArray_GET_SIZE()
* PyBytes_AS_STRING()
* PyBytes_GET_SIZE()

Limited C API version 3.11 no longer casts arguments.

Add _PyBytes_CAST() and _PyByteArray_CAST() macros.