feat(@schematics/angular): set up fake timers in beforeEach instead of beforeAll

When migrating `fakeAsync` to vitest fake timers, fake timers were setup in `beforeAll` to support `fakeAsync` usage in `beforeAll` / `afterAll` hooks.
This was sacrificing timers isolation between tests.
This change resets fake timers between tests.
Any usage of fake timers APIs in `beforeAll` or `afterAll` hooks will fail.