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 94.19%. Comparing base (da115c7) to head (1620861).
Report is 1 commits behind head on master.

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   94.19%   94.19%           
=======================================
  Files         149      149           
  Lines       15888    15896    +8     
=======================================
+ Hits        14965    14974    +9     
+ Misses        923      922    -1     

Flag	Coverage Δ
eof_execution_spec_tests	17.31% <45.28%> (+0.06%)	⬆️
ethereum_tests	27.38% <47.16%> (+0.05%)	⬆️
ethereum_tests_silkpre	19.18% <25.00%> (+0.04%)	⬆️
execution_spec_tests	20.48% <47.16%> (+0.05%)	⬆️
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	86.30% <87.50%> (-0.10%)	⬇️

... and 1 file with indirect coverage changes