Text box formatter

A terminal UI prints each message inside its own ASCII box, with the boxes stacked vertically. Implement

format_boxes(sentences: list[str], max_width: int | None = None) -> list[str]

returning the output lines. Every sentence is a non-empty string of printable ASCII characters (spaces included).

Width. Every box is equally wide: its inner width W equals the longest sentence's length. If max_width is given (>= 1), W = min(longest, max_width).

Lines.

• A border line is "+" + "-" * (W + 2) + "+".
• A text line is "| " + text + " " * (W - len(text)) + " |" (text left-aligned, padded on the right to W).
• Output: a border, then the text lines of sentence 1, a border, the text lines of sentence 2, a border, and so on, ending with a border. Neighbouring boxes share the border between them. No sentences means no lines at all.

Wrapping. A sentence of length <= W is one text line, exactly as given (its spaces are kept). A longer sentence (only possible with max_width) is wrapped:

1. Split it into words at spaces; runs of spaces separate words and are otherwise dropped.
2. Cut any word longer than W into pieces of W characters (the last piece may be shorter); each piece counts as a word.
3. Fill lines greedily: put words on the current line separated by one space while the line stays <= W long; otherwise start a new line with that word.

If a long sentence has no words at all (it is only spaces), it becomes one empty text line.

format_boxes(["Hello there", "Hi"])
# ["+-------------+",
#  "| Hello there |",
#  "+-------------+",
#  "| Hi          |",
#  "+-------------+"]

format_boxes(["the quick brown fox", "ok"], max_width=9)
# ["+-----------+",
#  "| the quick |",
#  "| brown fox |",
#  "+-----------+",
#  "| ok        |",
#  "+-----------+"]

format_boxes(["abcdefghij  xy"], max_width=4)
# ["+------+",
#  "| abcd |",
#  "| efgh |",
#  "| ij   |",      ("ij xy" would be 5 > 4)
#  "| xy   |",
#  "+------+"]