Replace per-character wrchar() loops in render_line/fill_row/help screens
with batched BIOS calls (bios_writeattr/bios_fillcharattr), and cache the
per-line index record (idx_get) instead of refetching it ~13 times per
rendered line — each refetch cost two W3 bank switches via bank_read().
Also fixes a pre-existing indexer bug: when word-wrap pushes a token that
starts with an emphasis/code marker (e.g. `_text_`) onto a new line, the
marker got re-scanned a second time during the wrap continuation, flipping
line_style back off and corrupting the rendered attribute of the next
word. Fixed by snapshotting line_style at the last seen space and rolling
back to that snapshot (both the saved continuation style and the live
scan state) when a wrap is taken.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
snark13
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