test: Wrap usage of state transition API

[chfast]

Wrap the usage of the state transition API from the evmone::state for tests so that the new API in evmone::test only exposes TestState and hides state::State.

This isolates usage of the evmone::state to lower the disturbance caused by API modifications,
e.g. in #802.

[codecov]

Codecov Report

Attention: Patch coverage is 96.22642% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.99%. Comparing base (335d056) to head (03b5bf6).

Files with missing lines	Patch %	Lines
test/blockchaintest/blockchaintest_runner.cpp	88.88%	1 Missing ⚠️
test/t8n/t8n.cpp	87.50%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1013   +/-   ##
=======================================
  Coverage   93.98%   93.99%           
=======================================
  Files         147      147           
  Lines       15588    15596    +8     
=======================================
+ Hits        14651    14660    +9     
+ Misses        937      936    -1     

Flag	Coverage Δ
eof_execution_spec_tests	17.61% <45.28%> (+0.06%)	⬆️
ethereum_tests	27.78% <47.16%> (+0.05%)	⬆️
ethereum_tests_silkpre	19.52% <25.00%> (+0.05%)	⬆️
execution_spec_tests	19.51% <47.16%> (+0.06%)	⬆️
unittests	88.98% <81.13%> (+0.02%)	⬆️

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

Files with missing lines	Coverage Δ
test/state/test_state.cpp	100.00% <100.00%> (ø)
test/state/test_state.hpp	80.00% <ø> (ø)
test/statetest/statetest_runner.cpp	96.66% <100.00%> (ø)
test/unittests/state_system_call_test.cpp	100.00% <100.00%> (ø)
test/unittests/state_transition.cpp	98.37% <100.00%> (+0.79%)	⬆️
test/blockchaintest/blockchaintest_runner.cpp	76.92% <88.88%> (-0.50%)	⬇️
test/t8n/t8n.cpp	86.80% <87.50%> (-0.10%)	⬇️

... and 1 file with indirect coverage changes