coverage: count number of executions per line #1977

Job	Run time
Build Echidna on ubuntu-20.04	21m 39s
Build Echidna on macos-13	37m 1s
Build Echidna on windows-latest	31m 37s
Test with solc 0.4.25 on ubuntu-latest	4m 58s
Test with solc 0.5.7 on ubuntu-latest	3m 33s
Test with solc 0.6.12 on ubuntu-latest	3m 44s
Test with solc 0.7.5 on ubuntu-latest	4m 9s
Test with solc 0.4.25 on windows-latest	3m 49s
Test with solc 0.5.7 on windows-latest	4m 5s
Test with solc 0.6.12 on windows-latest	4m 41s
Test with solc 0.7.5 on windows-latest	4m 25s
	2h 3m 41s

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