* Cleanup imports and update module docstring.
* Simplify detection of SIMD support.
* Correctly guard `update()` cases.
* Rewrite `py_blake2b_or_s_new` and rename it to `py_blake2_new`.
* Rewrite `blake2_blake2b_copy_locked` and `py_blake2_clear`.
* Refactor computations of `digest` and `hexdigest`.
* Simplify `py_blake2b_get_name` and `py_blake2b_get_block_size`.
* Add `hacl_get_blake2_info` to extract static BLAKE-2 information.
This new helper is used by `py_blake2b_get_digest_size`, but can
be later used to expose `key_length` more easily.
OpenSSL and HACL*-based hash functions constructors now support both `data` and `string` parameters.
Previously these constructor functions inconsistently supported sometimes `data` and sometimes `string`,
while the documentation expected `data` to be given in all cases.
This replaces the existing hashlib Blake2 module with a single implementation that uses HACL\*'s Blake2b/Blake2s implementations. We added support for all the modes exposed by the Python API, including tree hashing, leaf nodes, and so on. We ported and merged all of these changes upstream in HACL\*, added test vectors based on Python's existing implementation, and exposed everything needed for hashlib.
This was joint work done with @R1kM.
See the PR for much discussion and benchmarking details. TL;DR: On many systems, 8-50% faster (!) than `libb2`, on some systems it appeared 10-20% slower than `libb2`.
