[core] Withdrawals

[yperbasis]

This PR implements to core part of EIP-4895: Beacon chain push withdrawals as operations. It does not implement necessary changes (if any) to the body downloader.

[codecov]

Codecov Report

Merging #822 (dd676d3) into master (b48e449) will increase coverage by 0.01%.
The diff coverage is 75.67%.

@@            Coverage Diff             @@
##           master     #822      +/-   ##
==========================================
+ Coverage   66.97%   66.99%   +0.01%     
==========================================
  Files         237      239       +2     
  Lines       18080    18192     +112     
  Branches     2758     2785      +27     
==========================================
+ Hits        12109    12187      +78     
- Misses       4901     4928      +27     
- Partials     1070     1077       +7     

Impacted Files	Coverage Δ
core/silkworm/consensus/engine.cpp	100.00% <ø> (+6.45%)	⬆️
core/silkworm/consensus/engine.hpp	100.00% <ø> (ø)
core/silkworm/consensus/pos/engine.hpp	100.00% <ø> (ø)
core/silkworm/types/block.hpp	0.00% <ø> (ø)
core/silkworm/types/withdrawal.hpp	0.00% <0.00%> (ø)
core/silkworm/types/block.cpp	82.66% <65.00%> (-4.96%)	⬇️
core/silkworm/types/withdrawal.cpp	76.19% <76.19%> (ø)
core/silkworm/consensus/base/engine.cpp	92.07% <88.00%> (-0.86%)	⬇️
core/silkworm/consensus/pos/engine.cpp	87.50% <90.00%> (-12.50%)	⬇️
core/silkworm/execution/processor.cpp	85.93% <100.00%> (+0.45%)	⬆️
... and 15 more

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