Word-wrap previously emitted a phantom whitespace-only row when a word
exactly filled a row and the input continued (e.g. "abcde fghij" at
width 5 wrapped to 3 rows instead of 2). Separator whitespace that does
not fit the remaining space is now handled like ratatui's WordWrapper
(trim: false): whitespace filling the remaining cells is dropped,
whitespace after an exactly full row is dropped one grapheme at a time,
and any leftover whitespace leads the next row.
wrapped_rows now keeps byte-accurate column bookkeeping so screen_map
round-trips hold for all visible positions; positions inside dropped
whitespace have no screen representation and are treated as such.
Verified differentially against ratatui 0.30's WordWrapper (a faithful
reference port cross-checked against the real Paragraph renderer):
row counts now match for single- and multi-space separators, trailing
whitespace, CJK and mixed-width inputs.
