Expose underlying Z3_context and Z3_sort #491

Job	Run time
check-formatting	8s
build_on_wasm	26m 19s
build_with_bundled_z3 (linux)	11m 36s
run_clippy	35s
build_with_bundled_z3 (macos)	10m 6s
build (macos-latest)	28s
build_with_vcpkg_installed_z3 (linux)	1m 40s
build_with_bundled_z3 (windows)	16m 57s
build_with_vcpkg_installed_z3 (macos)	2m 1s
build (ubuntu-latest)	38s
build_with_vcpkg_installed_z3 (windows)	5m 59s
	1h 16m 27s

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