Periodically print Z3 statistics #7001

Job	Run time
compiler-warnings	2m 14s
build-mdbook	5s
format-check	3m 47s
docker-tests	20m 56s
integration-tests (ubuntu-latest, oopsla19)	18m 57s
integration-tests (ubuntu-latest, arrays)	10m 3s
scaladoc-check	2m 12s
unit-tests (ubuntu-latest)	4m 45s
integration-tests (macos-latest, oopsla19)	15m 44s
unit-tests (macos-latest)	3m 10s
	1h 21m 53s

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