Improve Dilithium (speed) verification stack usage

[mkannwischer]

Once upon a time, we wrote a paper on memory-efficient Dilithium [1] which included a speed-optimized version of verification that still included some memory optimizations that don't come at a performance penalty.

Unfortunately with the update of the reference code to round 3 that version did not get migrated leading to some complaints about verification memory consumption.

I finally found some time to port these. Verficication speed is essentially unchanged, but stack consumption is much better.

[1] https://eprint.iacr.org/2020/1278

The change is essentially this: before	Scheme	Implementation	Key Generation [bytes]	Sign [bytes]	Verify [bytes]
dilithium2	clean	38,304	51,968	36,192
dilithium2	m4f	38,296	49,416	36,220
dilithium2	m4fstack	4,408	5,072	2,704
dilithium3	clean	60,832	79,616	57,728
dilithium3	m4f	60,824	68,864	57,720
dilithium3	m4fstack	4,408	6,608	2,704
dilithium5	clean	97,696	122,724	92,940
dilithium5	m4f	97,688	116,076	92,932
dilithium5	m4fstack	4,408	8,136	2,712

after	Scheme	Implementation	Key Generation [bytes]	Sign [bytes]	Verify [bytes]
dilithium2	clean	38,304	51,968	36,192
dilithium2	m4f	38,296	49,416	9,012
dilithium2	m4fstack	4,408	5,072	2,704
dilithium3	clean	60,832	79,616	57,728
dilithium3	m4f	60,824	68,864	9,880
dilithium3	m4fstack	4,408	6,608	2,704
dilithium5	clean	97,696	122,724	92,940
dilithium5	m4f	97,688	116,076	11,944
dilithium5	m4fstack	4,408	8,136	2,712

[mkannwischer]

See https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/F4-PyxwFD_g/m/098dlKP8AQAJ

[mkannwischer]

Since there were no objections in the last month, I'm going to merge this now.