lib/crypto: tests: Add KUnit tests for MD5 and HMAC-MD5

Add a KUnit test suite for the MD5 library functions, including the
corresponding HMAC support.  The core test logic is in the
previously-added hash-test-template.h.  This commit just adds the actual
KUnit suite, and it adds the generated test vectors to the tree so that
gen-hash-testvecs.py won't have to be run at build time.

Link: https://lore.kernel.org/r/20250805222855.10362-8-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@kernel.org>