scan() returns matches in top-to-bottom reading order. With the
26-label cap, that meant the first 26 matches on screen ate all the
labels — your cursor could be at the bottom of the buffer and still
have no labels near it.
Sort matches by |line - cursor_line|, then by |col - cursor_col| as
tie-break, before label assignment. Labels now land on the 26 closest
matches rather than the 26 topmost. Same label pool, same public API,
big UX win for any buffer with more hits than labels.