coverage: count number of executions per line #1979

Job	Run time
Build Echidna on ubuntu-20.04	5m 24s
Build Echidna on macos-13	36m 16s
Build Echidna on windows-latest	13m 21s
Test with solc 0.4.25 on ubuntu-latest	5m 2s
Test with solc 0.5.7 on ubuntu-latest	3m 38s
Test with solc 0.6.12 on ubuntu-latest	4m 0s
Test with solc 0.7.5 on ubuntu-latest	4m 0s
Test with solc 0.4.25 on windows-latest	4m 3s
Test with solc 0.5.7 on windows-latest	3m 51s
Test with solc 0.6.12 on windows-latest	5m 16s
Test with solc 0.7.5 on windows-latest	5m 4s
	1h 29m 55s

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