patches: fix O(position) lag — O(1) fast path in charposForAccessibilityIndex:

charposForAccessibilityIndex: walked composed character sequences
from the start of a visible run to the target AX index.  For a run
covering an entire ASCII buffer, this is O(cursor_position): moving
to line 10,000 requires ~500,000 iterations per call.

The method is called on every SelectedTextChanged notification
response (accessibilityBoundsForRange: from the AX server for cursor
tracking), making cursor movement O(position) in large files.

Fix: when ax_length == length for a run (all characters are single
AX index units — true for all ASCII/Latin text), the charpos offset
is simply ax_idx - run.ax_start.  O(1) instead of O(position).

Multi-byte runs (emoji, CJK, non-BMP) fall back to the sequence walk,
bounded by run length (visible window size), not total buffer size.

patches/0006-doc-add-VoiceOver-accessibility-section-to-macOS-app.patch

@@ -1,7 +1,7 @@
-From ca89e85f199e054a6cef6272425d2920e55b2ea5 Mon Sep 17 00:00:00 2001
+From 4341052ad931a98b8453368753b596e7743132b8 Mon Sep 17 00:00:00 2001
 From: Martin Sukany <martin@sukany.cz>
 Date: Sat, 28 Feb 2026 12:58:11 +0100
-Subject: [PATCH 7/9] doc: add VoiceOver accessibility section to macOS
+Subject: [PATCH 6/8] doc: add VoiceOver accessibility section to macOS
  appendix
 
 * doc/emacs/macos.texi (VoiceOver Accessibility): New node.  Document