Fix for third party block reuse

[Geal]

This changes the third party block signature format to prevent reuse of third party blocks across tokens, by including the previous block's signature in the signed data

[Geal]

I'm not decided yet on the best name for the functions still allowing the old format, between Biscuit::unsafe_deprecated_deserialize and UnverifiedBiscuit::unsafe_from

[codspeed-hq]

CodSpeed Performance Report

Merging #230 will not alter performance

_{Comparing geal/third-party-reuse (4c2b1ad) with v5 (e59f41d)}

Summary

✅ 12 untouched benchmarks

[divarvel]

I'm not decided yet on the best name for the functions still allowing the old format, between Biscuit::unsafe_deprecated_deserialize and UnverifiedBiscuit::unsafe_from

I’d go for the most explicit. I read unsafe_from in the diff and was a bit confused

[divarvel]

I think we should document the signature scheme to make a few things clearer:

• imo the version should be signed (if defined)
• the previous key should not be signed if we sign the previous signature instead

[codecov]

Codecov Report

Attention: Patch coverage is 87.17949% with 15 lines in your changes missing coverage. Please review.

Project coverage is 69.70%. Comparing base (d90accd) to head (4c2b1ad).
Report is 1 commits behind head on v5.

Files with missing lines	Patch %	Lines
biscuit-auth/src/crypto/mod.rs	90.19%	5 Missing ⚠️
biscuit-auth/src/token/unverified.rs	69.23%	4 Missing ⚠️
biscuit-auth/src/token/third_party.rs	70.00%	3 Missing ⚠️
biscuit-auth/src/format/mod.rs	94.28%	2 Missing ⚠️
biscuit-auth/src/token/mod.rs	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v5     #230      +/-   ##
==========================================
+ Coverage   68.96%   69.70%   +0.74%     
==========================================
  Files          25       25              
  Lines        5922     5945      +23     
==========================================
+ Hits         4084     4144      +60     
+ Misses       1838     1801      -37     

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