[gephi-lite] Adds layout orchestration tests

Details:
- Mocks side effects used in layouts/index.ts, using vi.hoisted and
  vi.mock
- Adds unit tests for startLayout (restart, stop, filter change,
  sync/worker interplay)
- Adds unit tests for buildLayoutGraph (positions, fixed nodes, edges,
  size)
- Adds unit tests for createLayoutSupervisor (sync, transform,
  getPositions, kill)

Author: jacomyal