New API prototype: StateView

[chfast]

The prototype of the new API for evmone. It uses the test runners as users and modifies the State API from state.h.

• the user provides read-only StateView interface with (simpler than State) representation of the State.
• the transaction execution (i.e. evmone via transition()) takes the StateView and produces StateDiff.
• user must apply the StateDiff to its StateView implementation.

[codecov[bot]]

Codecov Report

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Additional details and impacted files

@@            Coverage Diff            @@
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  Coverage          ?   32.40%           
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  Files             ?      110           
  Lines             ?     9862           
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  Hits              ?     3196           
  Misses            ?     6666           
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Flag	Coverage Δ
blockchaintests	59.88% <ø> (?)
statetests	63.14% <95.71%> (?)
statetests-silkpre	25.50% <31.17%> (?)

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Files	Coverage Δ
test/blockchaintest/blockchaintest.hpp	0.00% <ø> (ø)
test/state/account.hpp	100.00% <100.00%> (ø)
test/state/host.cpp	100.00% <100.00%> (ø)
test/state/mpt_hash.cpp	100.00% <100.00%> (ø)
test/state/mpt_hash.hpp	100.00% <ø> (ø)
test/state/state.hpp	100.00% <100.00%> (ø)
test/statetest/statetest_loader.cpp	78.54% <100.00%> (ø)
test/statetest/statetest_runner.cpp	69.23% <100.00%> (ø)
test/unittests/state_transition.hpp	0.00% <ø> (ø)
test/utils/utils.cpp	68.00% <100.00%> (ø)
... and 13 more