hmac: improve bytes handling

[sobolevn]

new and HMAC.__init__ accepts bytes | bytearray as the first argument: https://github.com/python/cpython/blob/87b5fd9d9de11c68b9940d3a1dba902138129109/Lib/hmac.py#L52

digest works with any ReadableBuffer:

>>> hmac.digest(bytearray(b''), bytearray(b''), 'md5')
b't\xe6\xf7)\x8a\x9c-\x16\x895\xf5\x8c\x00\x1b\xad\x88'
>>> hmac.digest(memoryview(b''), memoryview(b''), 'md5')
b't\xe6\xf7)\x8a\x9c-\x16\x895\xf5\x8c\x00\x1b\xad\x88'

>>> hmac.digest(bytearray(b''), memoryview(b''), 'md5')
b't\xe6\xf7)\x8a\x9c-\x16\x895\xf5\x8c\x00\x1b\xad\x88'
>>> hmac.digest(memoryview(b''), bytearray(b''), 'md5')
b't\xe6\xf7)\x8a\x9c-\x16\x895\xf5\x8c\x00\x1b\xad\x88'

And has len() call on itself: https://github.com/python/cpython/blob/87b5fd9d9de11c68b9940d3a1dba902138129109/Lib/hmac.py#L214

Refs #9006

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉