Update draft 06

[TJ-91]

This PR updates to the newest PQC draft version, as well as fixes v6 signature salt.

V6 / RFC 9580

• correctly implement v6 salt for document signatures (was only properly working for key signatures before)
  • change HashList for use with salt
  • implement v6 OPS with salt
  • gracefully fail when verifying v6 cleartext signatures by skipping them. Due to the salt that is detected at the end, two passes are required which requires further changes to the code.
• add Ed448/X448 standalone algorithms

PQC

• final PQC NIST standard algorithms
• update to PQC draft version 06: KEM Combiner, SLH-DSA parameters, Test Vectors, ...
  • -06 is not-yet published but will be -05 with fixed test vectors
• Add X448 and Ed448 for composite PQC combinations

Botan

• Both ENABLE_CRYPTO_REFRESH and ENABLE_PQC now require Botan 3.6.
  • Ed448/X448 only available from 3.4
  • ML-KEM / ML-DSA / SLH-DSA final NIST standards available from Botan 3.6
  • Supporting partial features from lower Botan versions would mean to either have lots of deprecation warnings or have special code for the different versions.

[codecov]

Codecov Report

Attention: Patch coverage is 95.74468% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.67%. Comparing base (9077b2d) to head (21c2f96).

Files with missing lines	Patch %	Lines
src/librepgp/stream-packet.cpp	93.33%	1 Missing ⚠️
src/librepgp/stream-sig.cpp	83.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2287   +/-   ##
=======================================
  Coverage   84.67%   84.67%           
=======================================
  Files         116      116           
  Lines       23436    23455   +19     
=======================================
+ Hits        19844    19861   +17     
- Misses       3592     3594    +2     

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