B1: Fix memory leak in ns_ax_scan_interactive_spans — [spans copy]
returned +1 retained object never released by caller.
Now returns [[spans copy] autorelease].
B2: Remove dead function ns_ax_utf16_length_for_buffer_range —
defined but never called anywhere in the patch.
B3: Add specpdl unwind protection in
EmacsAccessibilityInteractiveSpan setAccessibilityFocused: —
if Fselect_window signals, block_input is now always matched
by unblock_input via record_unwind_protect_void.
W2: Document ns_ax_event_is_line_nav_key fragility in README
Known Limitations (raw keycodes vs command symbols).
W4: Add comment for #include intervals.h (TEXT_PROP_MEANS_INVISIBLE).
M3: accessibilityBoundsForRange: on EmacsView now delegates to the
focused EmacsAccessibilityBuffer for accurate per-range geometry,
with cursor-rect fallback for Zoom.
M4: Add <NSAccessibility> protocol conformance to
EmacsAccessibilityBuffer @interface declaration.
W1: Expanded commit message listing all new types, functions, DEFSYM
additions, and threading model.
