blockchaintest: Add support for revision transitions

[chfast]

Add support for blockchain tests with predefined timestamp of a revision transition (e.g. transtion from Shanghai to Cancun at the timestamp of 15000).

[codecov]

Codecov Report

Merging #736 (3997e32) into master (f6d6ec3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #736   +/-   ##
=======================================
  Coverage   97.79%   97.79%           
=======================================
  Files         109      109           
  Lines       10295    10303    +8     
=======================================
+ Hits        10068    10076    +8     
  Misses        227      227           

Flag	Coverage Δ
blockchaintests	60.79% <ø> (ø)
statetests	60.83% <ø> (ø)
statetests-silkpre	26.27% <0.00%> (-0.03%)	⬇️
unittests	95.90% <100.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
test/blockchaintest/blockchaintest.hpp	0.00% <ø> (ø)
test/blockchaintest/blockchaintest_loader.cpp	94.87% <100.00%> (ø)
test/unittests/blockchaintest_loader_test.cpp	100.00% <100.00%> (ø)
test/utils/utils.cpp	64.86% <100.00%> (+5.48%)	⬆️
test/utils/utils.hpp	100.00% <100.00%> (ø)