ci(core): Reduce memory usage in tests (part-2) (no-changelog) (#7671)

This also gets rid of `Db.collection`, which was another source of
circular dependencies.

packages/cli/test/shared/mocking.ts

@@ -0,0 +1,12 @@
+import { Container } from 'typedi';
+import { mock } from 'jest-mock-extended';
+import type { DeepPartial } from 'ts-essentials';
+
+export const mockInstance = <T>(
+	ctor: new (...args: unknown[]) => T,
+	data: DeepPartial<T> | undefined = undefined,
+) => {
+	const instance = mock<T>(data);
+	Container.set(ctor, instance);
+	return instance;
+};