Migrate to ESPtool 4.x

[marcelstoer]

ESPtool v3 only receives patches critical bugs and we should move to v4.

(Un)fortunately, the internal structure we had to rely upon until now was completely refactored. ESPtool now offers a public API: https://github.com/espressif/esptool/releases/tag/v4.0. That's most welcome (I had asked for this for years) but it also means a bit of a migration effort I guess.

[DeeEmm]

The code is already working on V4. I suspect that V4 is backwards compatible with V3