lib/signature: implement personal_recover (eip 191)

[q9f]

ref #15

Eth::Signature.personal_recover message, signature, chain_id

• moved from Eth::Key to Eth::Signature namespace because recovering Signatures work without known keys
• added support for chain IDs (EIP 155)

works entirely with rbsecp256k1 (no openssl)

[codecov-commenter]

Codecov Report

Merging #21 (5716bbb) into main (80c27fe) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #21   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        13    +2     
  Lines          390       433   +43     
=========================================
+ Hits           390       433   +43     

Impacted Files	Coverage Δ
lib/eth.rb	100.00% <100.00%> (ø)
lib/eth/address.rb	100.00% <100.00%> (ø)
lib/eth/chains.rb	100.00% <100.00%> (ø)
lib/eth/signature.rb	100.00% <100.00%> (ø)
spec/eth/chains_spec.rb	100.00% <100.00%> (ø)
spec/eth/signature_spec.rb	100.00% <100.00%> (ø)

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