hashtable.h: Py_uhash_t and _PyHASH_MULTIPLIER were added in Python 3.2
Fix alignment issue on 64-bit platforms

Issue #20354: Fix alignment issue in the tracemalloc module on 64-bit
platforms. Bug seen on 64-bit Linux when using "make profile-opt".

Only align the "frame_t" structure on 32-bit when Visual Studio is used.
Before the alignment to 32-bit was applied to the whole file any
compiler supporting "#pragma pack(4)" which includes GCC.
Fix slicing traces and fix slicing a traceback.
Python issue #20616: Add a format() method to tracemalloc.Traceback.