EOF RETURNDATA* to pad on OOB read

[pdobacz]

Closes #896, implements ipsilon/eof#90 / ethereum/EIPs#8617 the simplest way - by checking two first bytes of code on every instructions.

A better version would be to store the result in ExecutionState, and the best to use an entirely different instruction table in dispatch functions.

Should we do the ExecutionState version right away now, or keep as is? Anyway, opening as draft until the EOF pr doesn't get merged (should be decided on the next eof impl call)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.33%. Comparing base (df16c70) to head (f976b45).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
+ Coverage   95.29%   95.33%   +0.03%     
==========================================
  Files         138      138              
  Lines       15485    15615     +130     
==========================================
+ Hits        14757    14887     +130     
  Misses        728      728              

Flag	Coverage Δ
ethereum_tests	26.77% <10.55%> (-0.18%)	⬇️
ethereum_tests_silkpre	18.53% <9.31%> (-0.10%)	⬇️
execution_spec_tests	18.07% <7.14%> (-0.11%)	⬇️
unittests	90.38% <100.00%> (+0.08%)	⬆️

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Files	Coverage Δ
lib/evmone/instructions.hpp	100.00% <100.00%> (ø)
test/unittests/evm_eof_calls_test.cpp	100.00% <100.00%> (ø)