Show gas per second in the UI #1960

Job	Run time
Build Echidna on ubuntu-20.04	5m 31s
Build Echidna on macos-13	43m 27s
Build Echidna on windows-latest	29m 39s
Test with solc 0.4.25 on ubuntu-latest	4m 54s
Test with solc 0.5.7 on ubuntu-latest	3m 40s
Test with solc 0.6.12 on ubuntu-latest	3m 34s
Test with solc 0.7.5 on ubuntu-latest	3m 55s
Test with solc 0.4.25 on windows-latest	4m 28s
Test with solc 0.5.7 on windows-latest	4m 7s
Test with solc 0.6.12 on windows-latest	3m 53s
Test with solc 0.7.5 on windows-latest	5m 56s
	1h 53m 4s

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