eof: Move type validation outside of header validation

[chfast]

This allows separate header and type validation and simplify the implementation of the former.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.23%. Comparing base (bbd7e03) to head (d304085).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1052      +/-   ##
==========================================
- Coverage   94.23%   94.23%   -0.01%     
==========================================
  Files         155      155              
  Lines       16004    15997       -7     
==========================================
- Hits        15082    15075       -7     
  Misses        922      922              

Flag	Coverage Δ
eof_execution_spec_tests	17.69% <100.00%> (-0.03%)	⬇️
ethereum_tests	27.46% <100.00%> (-0.03%)	⬇️
ethereum_tests_silkpre	19.31% <0.00%> (+<0.01%)	⬆️
execution_spec_tests	20.56% <0.00%> (+<0.01%)	⬆️
unittests	89.03% <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	85.46% <100.00%> (-0.18%)	⬇️

[pdobacz]

LGTM. Such refactor was considered earlier. I completely don't recall the reasons why this didn't go through back then. Looks all good now 🤷

[chfast]

I think #1034 was a prerequisite. I fuzzed these two PRs.