fix(crypto-transaction): reject non-canonical rlp encodings

[oXtxNt9U]

Summary

The transaction deserializer accepted some encodings that re-serialize to different bytes. Nodes rebuild stored transactions with the serializer when serving blocks, so a validator could commit a block whose served bytes no longer match its payloadSize, and syncing nodes would reject that block forever.

Fixes

• Reject an 11th RLP field. The field-count guard was off by one.
• Reject an empty legacy second signature field. It was treated as "no signature".
• Decode RLP lengths without 32-bit overflow. << wrapped overlong length prefixes to valid lengths.

Tests

• A unit test for each fix.
• deserializer.fuzz.test.ts: a seeded fuzz test checking that every accepted encoding re-serializes to identical bytes. It runs 10,000 random cases plus fixed boundary inputs. FUZZ_SEED / FUZZ_RUNS reproduce a failure or run a longer campaign.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.62%. Comparing base (c39bb16) to head (abf63b3).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1521      +/-   ##
===========================================
+ Coverage    80.31%   80.62%   +0.31%     
===========================================
  Files          952      963      +11     
  Lines        17162    17620     +458     
  Branches      2599     2698      +99     
===========================================
+ Hits         13784    14207     +423     
- Misses        3373     3405      +32     
- Partials         5        8       +3     

Flag	Coverage Δ
contracts	91.95% <ø> (?)
packages	80.34% <100.00%> (+0.02%)	⬆️

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