ML-KEM: fix comments, API signatures, minor issues #6394

Job	Run time
build library (--disable-asm --enable-mlkem --enable-lms --enable-xmss --enable-mldsa)	36s
build library (--disable-asm)	36s
build library (--disable-asm --enable-all-crypto --enable-mlkem --enable-lms --enable-xmss --enab...	56s
build library (--enable-intelasm --enable-sp-asm --enable-mlkem --enable-lms --enable-xmss --enab...	34s
build library (--enable-intelasm --enable-sp-asm --enable-all-crypto --enable-mlkem --enable-lms ...	49s
build library (--enable-intelasm --enable-sp-asm)	35s
	4m 6s

Provide feedback