chore(specs): add final decorator

[SamWilsn]

🗒️ Description

mypyc can use the @final decorator for optimizations, so might as well add it.

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[codecov]

Codecov Report

❌ Patch coverage is 94.36997% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.52%. Comparing base (d7def91) to head (b503630).

Files with missing lines	Patch %	Lines
src/ethereum/trace.py	0.00%	10 Missing ⚠️
src/ethereum/merkle_patricia_trie.py	0.00%	4 Missing ⚠️
src/ethereum/state.py	0.00%	4 Missing ⚠️
src/ethereum/genesis.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #2934      +/-   ##
===================================================
+ Coverage            90.49%   90.52%   +0.02%     
===================================================
  Files                  535      535              
  Lines                32430    32712     +282     
  Branches              3012     3012              
===================================================
+ Hits                 29349    29613     +264     
- Misses                2563     2581      +18     
  Partials               518      518              

Flag	Coverage Δ
unittests	90.52% <94.36%> (+0.02%)	⬆️

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