Fix sync-less doorbell discovery on shared networks

[gal-nir]

Summary

• Fixes discovery for sync-less doorbells when a sync-less mini exists on the same network ID.
• Uses homescreen parsing helpers for minis/doorbells (including alternate doorbell payload keys like lotus).
• Only treats a device as "attached to sync module" when a real sync module exists for that network.
• Prevents camera-list merge drops when a network is absent from camera/usage.
• Adds regression tests for alternate homescreen keys and sync-less doorbell behavior.

Reproduction

• Account with:
  • Blink Mini (sync-less)
  • Blink Doorbell (sync-less)
• Both appear in homescreen.
• camera/usage returns empty cameras list for that network.

Before

• Only mini appeared in blink.cameras.
• Doorbell was skipped.

After

• Both mini and doorbell appear in blink.cameras.
• Doorbell supports existing BlinkLotus flow correctly.

Test plan

• Existing device listing script shows both devices.
• Doorbell appears under cameras and doorbell listing.
• New/updated unit tests cover:
  • alternate homescreen key (lotus)
  • sync-less doorbell with empty camera/usage
  • attached-to-sync behavior requiring sync_modules presence.