Various fixes applied. See PR for more details.

[ChrisMenning]

Fixes applied

1. paginate_html — per-word Image allocation (epub_reader_controller.py)
   A fresh Image.new("1", (1, 1)) + ImageDraw.Draw(...) was created for every word during word-wrap measurement. A single _measure_draw object is now created once per call and reused — eliminating thousands of object allocations per chapter.

2. _extract_pages — entire book paginated at startup (epub_reader_controller.py)
   All chapters were paginated upfront before showing anything. Now only the first chapter is loaded; next_page / prev_page already had chapter-transition logic that was dead code — it's now live. load_chapter() caches chapters to avoid re-paginating on revisit.

3. display_Partial — sends full 48 000-byte frame over SPI (epd7in5_V2.py)
   The buffer was allocated as int(self.width * self.height / 8) (full frame) and transmitted in full over SPI even for a tiny radio-button region. It now allocates and sends only Width × Height bytes for the actual region.

4. init_part() called on every encoder tick (epaper_display_output.py, reader_modal_view.py)
   init_part() performs a hardware reset + full SPI init sequence. It was called on every rotary encoder step. Both call sites now guard with if _display_mode != "partial" so the hardware is only initialised once when entering partial mode.

5. _display_mode tracking + ensure_full_mode() (epaper_display_output.py, tomereader.py)
   EPaperDisplay now tracks display mode ("full" / "partial"). A new ensure_full_mode() method reinitialises hardware only when actually switching back from partial mode, replacing the two display.init_display() calls after modal close that triggered a full e-paper clear+reinit (and visible blank-flash) unconditionally.

6. CBZReaderView — 4-gray mode on a 1-bit framebuffer (cbz_reader_view.py)
   The CBZ reader called update_display(mode="4gray"), which is significantly slower than 1-bit mode. The display framebuffer is Image.new("1", ...), so pasting onto it already converts to binary — the 4-gray encode loop runs for no quality benefit. Changed to mode="1".

7. show_page() — re-parses chapter HTML on every page turn (epub_reader_controller.py)
   show_page() called BeautifulSoup(item.get_content(), ...) and searched headings on every single page turn just to populate the footer title. Results are now stored in _chapter_title_cache and parsed at most once per chapter.

8. cbz_reader_view.py — display_page now composes a fresh "L"-mode canvas locally, pastes the grayscale page onto it, draws the footer directly on that canvas, then passes it to the new display_gray_direct() method. The 1-bit shared framebuffer is never touched.

9. epaper_display_output.py — new display_gray_direct(img_L) method rotates the L-mode image and sends it straight to display_4Gray / getbuffer_4Gray, preserving all gray levels end-to-end.