gh-144995: Optimize memoryview == memoryview (#144996)

Optimize memoryview comparison: a memoryview is equal to itself, there is no
need to compare values, except if it uses float format.

Benchmark comparing 1 MiB:

    from timeit import timeit
    with open("/dev/random", 'br') as fp:
        data = fp.read(2**20)
    view = memoryview(data)
    LOOPS = 1_000
    b = timeit('x == x', number=LOOPS, globals={'x': data})
    m = timeit('x == x', number=LOOPS, globals={'x': view})
    print("bytes %f seconds" % b)
    print("mview %f seconds" % m)
    print("=> %f time slower" % (m / b))

Result before the change:

    bytes 0.000026 seconds
    mview 1.445791 seconds
    => 55660.873940 time slower

Result after the change:

    bytes 0.000026 seconds
    mview 0.000028 seconds
    => 1.104382 time slower

This missed optimization was discovered by Pierre-Yves David
while working on Mercurial.

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>