Apply some clippy lint where it makes sense

[ptondereau]

No big deals here, and just applying some clippy rules that make sense. Please don't hesitate to close if it's not relevant

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #226 will not alter performance

_{Comparing ptondereau:clippy-hunt (9043f42) with main (71f4350)}

Summary

✅ 12 untouched benchmarks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.

Project coverage is 67.51%. Comparing base (71f4350) to head (9043f42).

Files	Patch %	Lines
biscuit-auth/src/token/builder.rs	16.66%	5 Missing :warning:
biscuit-quote/src/lib.rs	0.00%	4 Missing :warning:
biscuit-auth/src/token/authorizer.rs	66.66%	3 Missing :warning:
biscuit-auth/src/datalog/mod.rs	83.33%	1 Missing :warning:
biscuit-auth/src/datalog/symbol.rs	50.00%	1 Missing :warning:
biscuit-auth/src/format/convert.rs	0.00%	1 Missing :warning:
biscuit-auth/src/token/authorizer/snapshot.rs	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #226 +/- ## ========================================== + Coverage 67.47% 67.51% +0.03% ========================================== Files 25 25 Lines 5347 5347 ========================================== + Hits 3608 3610 +2 + Misses 1739 1737 -2 ```

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[Geal]

thanks!