refactor: remove repetitive folds in `Z3Context` #7044

Job	Run time
compiler-warnings	2m 31s
docker-tests	21m 8s
build-mdbook	7s
format-check	3m 57s
integration-tests (ubuntu-latest, oopsla19)	18m 46s
integration-tests (ubuntu-latest, arrays)	10m 45s
scaladoc-check	2m 58s
integration-tests (macos-latest, oopsla19)	16m 51s
unit-tests (ubuntu-latest)	5m 27s
unit-tests (macos-latest)	4m 17s
	1h 26m 47s

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