Add pq native recipient and identity

[str4d]

Currently blocked on RustCrypto/KEMs#364 (the x-wing crate permits non-contributory behaviour for the X25519 subpart, while Filippo's Go impl does not, and we need to figure out where the correct fix goes).

[codecov]

Codecov Report

❌ Patch coverage is 70.58824% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.70%. Comparing base (8d79deb) to head (a221f3e).

Files with missing lines	Patch %	Lines
age/src/native/pq.rs	76.05%	17 Missing ⚠️
age/src/identity.rs	58.62%	12 Missing ⚠️
age/src/cli_common/recipients.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #632      +/-   ##
==========================================
+ Coverage   56.47%   56.70%   +0.22%     
==========================================
  Files          45       46       +1     
  Lines        4478     4557      +79     
==========================================
+ Hits         2529     2584      +55     
- Misses       1949     1973      +24     

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[fgsch]

Thank you! I've just started using this branch in my project and it's been working great.

I noticed rage-keygen still generates X25519 keys. Should it switch to PQ by default or have an option to generate PQ keys?

[str4d]

Yes, I will be switching the default to PQ in this PR. I have most of the associated changes for that locally; the main thing I'm blocking on for that is the design of the flags (age-keygen went with a -pq flag but that was when it wasn't the default).