refactor: implement Index<LeafExecutionPath> for ExecutionGraph (#162) #437

Job	Run time
Test (windows-latest, x86_64-pc-windows-msvc)	7m 28s
Format and Check Deps	1m 32s
Test (namespace-profile-mac-default, aarch64-apple-darwin)	1m 17s
Test (ubuntu-latest, x86_64-unknown-linux-gnu)	3m 55s
Test (namespace-profile-mac-default, x86_64-apple-darwin)	2m 41s
done	3s
	16m 56s

Provide feedback