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[bot]]

CodSpeed Performance Report

Merging #230 will not alter performance

_{Comparing geal/third-party-reuse (c026d50) 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[bot]]

Codecov Report

Attention: Patch coverage is 87.34940% with 21 lines in your changes missing coverage. Please review.

Project coverage is 69.89%. Comparing base (3930767) to head (c026d50). Report is 2 commits behind head on v5.

Files with missing lines	Patch %	Lines
biscuit-auth/src/crypto/mod.rs	88.88%	9 Missing :warning:
biscuit-auth/src/format/mod.rs	92.72%	4 Missing :warning:
biscuit-auth/src/token/unverified.rs	69.23%	4 Missing :warning:
biscuit-auth/src/token/third_party.rs	66.66%	3 Missing :warning:
biscuit-auth/src/token/mod.rs	87.50%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##               v5     #230      +/-   ##
==========================================
+ Coverage   69.03%   69.89%   +0.86%     
==========================================
  Files          25       25              
  Lines        5926     5990      +64     
==========================================
+ Hits         4091     4187      +96     
+ Misses       1835     1803      -32     

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