feat(odf): write a date and a time into an ods cell

[andiwand]

🤖 Generated with Claude Code

Step 2 of the typed-dates plan (decision 18, the ods half).

Change

• writable takes a date or time value that states its number. One without a number is still refused, before the cell changes.
• A date: office:value-type="date" and office:date-value, either YYYY-MM-DD or YYYY-MM-DDTHH:MM:SS when it has a time of day. number_format::civil_from_days turns the days back into a civil date.
• A time: office:value-type="time" and office:time-value as a duration, PT18H30M00S, with hours past 24 where the value runs over a day.
• The text: shown_number becomes shown_value. A date or time takes its text:p from the cell's date or time data style, and a number from its number style. A cell whose data style is of the other kind, or which has none, keeps the typed text.
• The time of day: a time, and a date below one day, go to the formatter as they are. The 1900 shift of serial_from_days would make a time of day negative, and the formatter then falls back to General. The LibreOffice probe below found that: 18:30 showed as -0.229166666666667 before the fix.

Review after the rebase

A date outside the years 1 to 9999 wrote an office:date-value that the reader refuses, and a very large number overflowed the calendar arithmetic. writable now refuses such a date, and a time that is not finite; a_date_past_9999_or_an_infinite_time_refuses covers both. civil_from_days returns std::uint32_t and has a qualified definition, as #976 now does. The rest holds: the floor of a negative day, the duration spelling, and the choice of a style by the category of the value.

Proof

• New OdfSheetWrite tests:
  • a date with a time, and a time, into cells without a style: exact markup, and the values read back;
  • the date op into a dd.mm.yyyy cell gives 02.01.2025;
  • a time into an hh:mm cell gives 18:30;
  • a date without its number is refused.
• OdfSheetWrite.*, OdfSheetValue.*, NumberFormat.*, Ooxml*, html.*, Csv* and the edit suites: 357 passed.
• LibreOffice oracle: LibreOffice converted an xlsx with dd.mm.yyyy, hh:mm and yyyy-mm-dd hh:mm cells to ods. back_translate wrote a date, a time, a date with a time, and a date into a plain cell. LibreOffice's csv export reads each value as written: 02.01.2025,18:30,2025-01-02 18:00,01/02/25 12:00 AM. Our text:p agrees for every styled cell. The plain cell keeps the typed 1/2/2025, while LibreOffice renders it in its own default date format.
• g++-15 -Wall -Wextra -Werror is clean on the touched files.