Add per-zone (partial) refresh for the IT8951 display

[pierrehenrymuller]

Hi,

Thanks a lot for this component, I've been using it daily on a reTerminal E1003.
Here are the per-zone refresh changes I added and validated on my hardware, hope they're useful to you.

Tested on Seeed reTerminal E1003 (10.3", 1872x1404) hardware.

Why

The component only did full-screen GC16 (visible flash, ~1s), fine for the deep-sleep art-frame, but not for an always-on dashboard with frequent updates.

What

• full_refresh(): the existing full-screen INIT+GC16 path (unchanged behaviour), now exposed publicly.

• render_framebuffer() + flush_zone(x, y, w, h, mode=1): render the framebuffer once, the push only a rectangle with a fast waveform (DU, no flash). Logical coordinates are mapped to panel coordinates (the buffer is X-mirrored) and x/width are aligned to 4 px (4bpp). A counter forces a full GC16 every N partials to clear ghosting.

• fill(Color) override using memset instead of the per-pixel base loop (~2.6M draw calls on this 1872x1404 panel) -> the per-frame auto-clear becomes ~instant.

Notes

• No change to the existing full-refresh behaviour; the new methods are opt-in, callable from a lambda (e.g. d(my_display).flush_zone(...)).

• DU is black/white; periodic GC16 (or the existing deghost) clears ghosting.

Good day

[pierrehenrymuller]

Example: a clock that updates every minute without flashing

Render the framebuffer once (cheap thanks to the memset fill()), then push only the rectangle that changed with flush_zone() — it uses the DU waveform, so there is no full-screen flash. Use full_refresh() (GC16) only occasionally, e.g. once a day, to clear any accumulated ghosting.

time:
  - platform: homeassistant
    id: ha_time
    on_time:
      - seconds: 0          # every minute
        then:
          - lambda: |-
              id(my_display).render_framebuffer();        // redraw RAM buffer (lambda)
              id(my_display).flush_zone(0, 0, 360, 120);  // push only the clock area (x,y,w,h) in DU

# Daily clean-up to clear ghosting from the partial (DU) updates:
# on_time -> at 05:00 -> id(my_display).full_refresh();