Rename ML-KEM and ML-DSA constants without underscore

• algorithms: centrally define KEM algorithm sizes in group entries

This switches to define the public key and ciphertext sizes of ML-KEM algorithms in gnutls_group_entry_st, instead of deriving those from the algorithm name at the usage in the TLS key shares.

• algorithms: rename GNUTLS_{PK,SIGN}ML_DSA* to GNUTLS__MLDSA

To be consistent with ML-KEM algorithms, omit underscores in ML-DSA gnutls_pk_algorithm_t and gnutls_sign_algorithm_t enum definitions, while keeping hyphens in the human readable names.

• algorithms: rename GNUTLS_PK_ML_KEM_* to GNUTLS_PK_MLKEM*

To be consistent with the naming of hybrid groups, omit underscores in the enum definition, while keeping hyphens in human readable names.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated / NEWS entry present (for non-trivial changes)
• CI timeout is 2h or higher (see Settings/CICD/General pipelines/Timeout)

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code