Fixes for pqc and crypto refresh

[TJ-91]

This includes the following fixes for the Crypto Refresh and PQC code:

• KMAC256::fixedInfo() now returns the correct value
• the v3 PKESK algorithm identifier byte is now included in the correct place (for X25519 and PQC)

Thanks to @teythoon for spotting the issues.

---

Further, I fixed a compile error (wrong variable used) for the Crypto Refresh / PQC code and included a copy constructor for the composite algorithms such that it will now build with MSVC/Clang.

A last change has been made to the salg parsing in the PKESK code. The variable was undefined (up to a certain point) and I initially set it to salg = PGP_SA_UNKNOWN;. In the Crypto Refresh code it is checked whether or not this is AES since v3 PKESK with the new algorithms don't encrypt the session key and requires AES for that case. This part of the logic is a bit messy currently since the salg value is defined early when it's not encrypted (can directly be parsed when the PKESKv3 material is parsed), but for other cases it's only available after decryption in encrypted_try_key().

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (9e5e13a) 77.26% compared to head (c551af4) 77.25%.

Files	Patch %	Lines
src/librepgp/stream-sig.cpp	85.71%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2142      +/-   ##
==========================================
- Coverage   77.26%   77.25%   -0.02%     
==========================================
  Files         194      194              
  Lines       37746    37751       +5     
==========================================
- Hits        29165    29163       -2     
- Misses       8581     8588       +7     

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[TJ-91]

For v6 it's mandated to have direct-key signatures.
This is what I implemented in 432e453:

• Add a direct-key signature only for v6 packets in pgp_generate_primary_key() (via new pgp_key_t::add_direct_sig() funciton).
• Leave the behaviour for old pgp versions as-is.
• Split rnp_selfsig_cert_info_t::populate() s.t. sig and uid can be populated independently. For direct-key signatures, only the signature part is relevant.
• For subkey / uid certification signatures the "preference subpackets" are not duplicated in other signatures

As far as I can see this implements the correct behaviour ("MUST") but not all of the Crypto Refresh's additional and optional subpackets etc.

[TJ-91]

I updated the branch (rebase on main) and fixed a typo (RNP_EXPERIMENTAL_CRYPTO_PQC to RNP_EXPERIMENTAL_PQC)

[ni4]

LGTM, thanks! We may safely ignore codecov failure as changed lines just throw exeption on malloc failure.