Add public key types for SLH-DSA (FIPS 205)

[Wind4Greg]

Hi it was great to see the ML-DSA keys added in PR #392, how can we get the SLH-DSA public keys added FIPS 205. These are detailed in Table 2 section 11. There are twelve variants:

SLH-DSA-SHA2-128s, SLH-DSA-SHAKE-128s, SLH-DSA-SHA2-128f, SLH-DSA-SHAKE-128f, SLH-DSA-SHA2-192s, SLH-DSA-SHAKE-192s, SLH-DSA-SHA2-192f, SLH-DSA-SHAKE-192f, SLH-DSA-SHA2-256s, SLH-DSA-SHAKE-256s, SLH-DSA-SHA2-256f, SLH-DSA-SHAKE-256f

Let me know how I can help. Best Regards Greg B.

[Wind4Greg]

Put in a PR instead per instructions. Whoops.