add support for ecdsa signatures

[Geal]

• Support for ECDSA signatures on curve secp256r1 biscuit#165

[codspeed-hq]

CodSpeed Performance Report

Merging #108 will not alter performance

_{Comparing fipscuit (c88fff0) with v5 (3e3f071)}

Summary

✅ 12 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 67.45407% with 124 lines in your changes are missing coverage. Please review.

Project coverage is 68.18%. Comparing base (3e3f071) to head (c88fff0).

Files	Patch %	Lines
biscuit-auth/src/crypto/ed25519.rs	53.16%	37 Missing ⚠️
biscuit-auth/src/crypto/p256.rs	54.05%	34 Missing ⚠️
biscuit-auth/src/crypto/mod.rs	78.49%	20 Missing ⚠️
biscuit-auth/src/token/unverified.rs	0.00%	16 Missing ⚠️
biscuit-auth/src/capi.rs	0.00%	4 Missing ⚠️
biscuit-parser/src/builder.rs	0.00%	4 Missing ⚠️
biscuit-auth/src/token/mod.rs	80.00%	3 Missing ⚠️
biscuit-auth/examples/third_party.rs	0.00%	2 Missing ⚠️
biscuit-auth/src/token/builder.rs	81.81%	2 Missing ⚠️
biscuit-auth/examples/testcases.rs	98.36%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##               v5     #108      +/-   ##
==========================================
+ Coverage   67.91%   68.18%   +0.27%     
==========================================
  Files          25       27       +2     
  Lines        5507     5689     +182     
==========================================
+ Hits         3740     3879     +139     
- Misses       1767     1810      +43     

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