All tests in basics/ directory can now run and pass using 64-bit unix
port with only a 16k heap (./run-tests --heapsize 16k). Tests in this
directory should remain small so they can be used for ports with a
small heap.
For these 3 bitwise operations there are now fast functions for
positive-only arguments, and general functions for arbitrary sign
arguments (the fast functions are the existing implementation).
By default the fast functions are not used (to save space) and instead
the general functions are used for all operations.
Enable MICROPY_OPT_MPZ_BITWISE to use the fast functions for positive
arguments.