device-install: Consistently use write-flash

[tyll]

Esptool accepts the write-flash command only on newer versions while older versions only accepted write_flash. Use write-flash consistently to avoid partial flashing with older esptool version.

🤝 Attestations

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