feat: Only do strict signature verification

[poljar]

There isn't a particular need to accept keys which are accepted by RFC8032. So let's just always do the strict signature verification.

[codspeed-hq]

Merging this PR will degrade performance by 11.28%

❌ 1 (👁 1) regressed benchmark
✅ 5 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
👁	Decrypting a message	186.2 µs	209.9 µs	-11.28%

---

_{Comparing poljar/strict-signatures-by-default (722c55f) with main (ee3c987)}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.35%. Comparing base (ee3c987) to head (722c55f).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #299      +/-   ##
==========================================
+ Coverage   91.33%   91.35%   +0.01%     
==========================================
  Files          34       34              
  Lines        4929     4927       -2     
  Branches     4929     4927       -2     
==========================================
- Hits         4502     4501       -1     
+ Misses        273      272       -1     
  Partials      154      154              

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