fix(fvm): accept malleable secp256k1 signatures (per EVM, etc.)

[Stebalien]

And add a test case.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.49%. Comparing base (bef9854) to head (9fbd582).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2156      +/-   ##
==========================================
+ Coverage   77.45%   77.49%   +0.03%     
==========================================
  Files         147      147              
  Lines       15709    15736      +27     
==========================================
+ Hits        12167    12194      +27     
  Misses       3542     3542              

Files with missing lines	Coverage Δ
shared/src/crypto/signature.rs	72.75% <100.00%> (+2.68%)	⬆️

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[rvagg]

yeah, ok, worth recording here that the context is mostly in RustCrypto/elliptic-curves#988, foundry-rs had a similar issue and it was resolved in revm which looks a lot like what we're implementing here: bluealloy/revm#870