Add functions for round trip decoding of transaction payloads

[peterbroadhurst]

We provide functions for serializing transactions in legacy-original, legacy-EIP155, and EIP-1559 flavors.

However, we don't currently provide the "recover" step - decoding the binary transaction (from eth_sendRawTransaction) according to the various applicable rules, and letting you recover the signature from it.

This PR adds that feature.

[awrichar]

Looks good. I didn't cross-check all of the decoding steps with the EIPs, but it looks correct to my recollection - and the symmetric encode/decode unit tests seem to be good validation on that.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.67%. Comparing base (39fe567) to head (3e5403b).

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #64      +/-   ##
===========================================
- Coverage   100.00%   99.67%   -0.33%     
===========================================
  Files           38       38              
  Lines         3317     3420     +103     
===========================================
+ Hits          3317     3409      +92     
- Misses           0       11      +11     

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