Decrease nodedb load delays over bluetooth, include prefetch, remove 20ms polling loop

[h3lix1]

• Refactored PhoneAPI node delivery so we keep a small prefetched queue of NodeInfo entries, clearing and refilling it across sessions; BLE reads now pop from this cache, immediately re-populate, and continue logging each node while moving on to the next.
• New prefetch path and consumption behaviour, and replaced meshtastic_NodeInfo_init_default assignment with value-initialisation
• Switched the FromRadio characteristic to support notifications, moved the read callback off the old 20 ms polling loop (!!)

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)
    Heltec (Lora32) V4