eof: Optimize EOF validation by using std::move

[chfast]

Optimize validate_instructions() by using std::move on arguments to returned InstructionValidationResult.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.21%. Comparing base (46dc5ee) to head (7d633bc).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1036   +/-   ##
=======================================
  Coverage   94.21%   94.21%           
=======================================
  Files         153      153           
  Lines       15933    15934    +1     
=======================================
+ Hits        15011    15012    +1     
  Misses        922      922           

Flag	Coverage Δ
eof_execution_spec_tests	17.53% <100.00%> (+<0.01%)	⬆️
ethereum_tests	27.34% <100.00%> (+<0.01%)	⬆️
ethereum_tests_silkpre	19.15% <0.00%> (ø)
execution_spec_tests	20.45% <0.00%> (-0.01%)	⬇️
unittests	89.00% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
lib/evmone/eof.cpp	85.71% <100.00%> (+0.02%)	⬆️