[schikani]

Python screens built from many put()/fill() calls cost Python time and
appeared piece by piece, because the desktop draws whatever has arrived every
10 ms. Measured on an ESP32-S3 with a full-screen 100x30 HMI (six screens):
a screen switch took 60–310 ms of Python time and 31–224 drawing requests,
while the serial link carried only 1–9 KB. The script was the bottleneck,
not the link or the desktop.

Changes

• Canvas pages: w.canvas(..., pages=n) keeps up to 16 pictures
  (tdui.MAX_PAGES) on the desktop.
  • draw_to(n) draws into a page while the window shows another.
  • show(n) shows a page whole, in one step.
  • copy_page(src, dst) copies a picture.
  • resize() keeps every page.
  • Drawing into a hidden page doesn't redraw the window.
• Big characters: canvas.big(x, y, text, fg, bg, scale, width) draws
  digits, A–Z and - + % / . : with half blocks, in one request (scale 1–4).
  width right-aligns the text and blanks the rest. tdui.big_size() gives
  the size.
• Cheaper drawing calls: put() and fill() call _tdui.send directly,
  two Python calls fewer each.
• More cells with PSRAM: tdui.MAX_CELLS counts every page. It's 32000 on
  boards with PSRAM and in the PC programs (192 KB at most, only while a
  script runs), and 2000 without PSRAM as before. tdui reads it from
  _tdui, and the error message gives the real number.
• Protocol: new requests TD_PYUI_PAGE, TD_PYUI_PAGE_COPY and
  TD_PYUI_BIG, added after the existing ones, so existing scripts are
  unchanged.
• Regenerated MicroPython: third_party/micropython is regenerated for
  the new tdui.py (MicroPython v1.29.0).

Result

With a page per screen and big(), the same HMI switches in 33–82 ms, and
each screen appears at once:

Page	Before	After
POWER	306 ms	68–82 ms
HOME	155 ms	45–50 ms
TEMPERATURE	109 ms	33–47 ms
STATUS	76 ms	40–63 ms

Testing

• PC build: all 13 tests pass, including the new tests/test_pyui.c
  (pages, copy, resize, big characters, the page and cell limits).
• Firmware builds: ESP32-S3, ESP32-C6 and classic ESP32 all build.
• On an ESP32-S3:
  • the HMI benchmark above;
  • its keypad drawn on a copy of the screen;
  • the documentation's example.

Docs: tinydesk-project.github.io, branch tdui-cells.