PyMem_Malloc() now uses the fast pymalloc allocator

PyMem_Malloc() now uses the fast pymalloc allocator

Issue #26249: PyMem_Malloc() allocator family now uses the pymalloc allocator
rather than system malloc(). Applications calling PyMem_Malloc() without
holding the GIL can now crash: use PYTHONMALLOC=debug environment variable to
validate the usage of memory allocators in your application.