lib/crypto: tests: Add KUnit tests for BLAKE2s

lib/crypto: tests: Add KUnit tests for BLAKE2s

Add a KUnit test suite for BLAKE2s.  Most of the core test logic is in
the previously-added hash-test-template.h.  This commit just adds the
actual KUnit suite, commits the generated test vectors to the tree so
that gen-hash-testvecs.py won't have to be run at build time, and adds a
few BLAKE2s-specific test cases.

This is the replacement for blake2s-selftest, which an earlier commit
removed.  Improvements over blake2s-selftest include integration with
KUnit, more comprehensive test cases, and support for benchmarking.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250827151131.27733-13-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>