MAML-format-specific validation: the declarative schema of every top-level MAML section and its allowed sub-keys plus the validator and its private helpers that check a raw MAML's section/sub-key names against it (presence only, not values); full-schema structural validation (parquet_validate_maml); cross-checking a user MAML against a base schema (parquet_validate_user_maml); loading MAML/qc-maml files from disk; and qc-maml field parsing/validation for read-time quality control. Merges what used to be parquet_metadata_sections.f90 and parquet_metadata_validate.f90.