NPOI was truncating sub-second values when formatting dates without a milliseconds specifier, while Excel rounds to the nearest second (e.g. 02:34:07.550 → 02:34:08). Additionally, on Linux systems with a broken NotoColorEmoji.ttf (missing loca table), SixLabors.Fonts throws MissingFontTableException during text measurement, crashing AutoSize and cell height calculations.

ExcelStyleDateFormatter: round seconds when no ms specifier

In ExcelStyleDateFormatter.Format(), round date up to the nearest second when:

• The pattern contains no millisecond specifiers (f, F, .0, .00, .000)
• The pattern contains no elapsed-time bracket symbols ([h], [m], [s], etc.) — elapsed-time formats derive hours/minutes/seconds directly from the raw double, so rounding the DateTime would corrupt the non-elapsed portions

bool hasMilliseconds = Pattern.Contains('f') || Pattern.Contains('F') || ...;
bool hasElapsedTime = Pattern.Contains(H_BRACKET_SYMBOL) || Pattern.Contains(M_BRACKET_SYMBOL) || ...;
if (!hasMilliseconds && !hasElapsedTime && date.Millisecond >= 500)
    date = date.AddMilliseconds(1000 - date.Millisecond);

SixLabors.Fonts: tolerate broken system fonts on Linux

• IFont2FontImpl: When no requested or Arial font is found, probe candidate system fonts with a test measurement and skip any that throw InvalidFontFileException (e.g. NotoColorEmoji with a missing loca table).
• GetDefaultCharWidth / GetCellWidth / GetContentHeight / GetRotatedContentHeight: Catch InvalidFontFileException and fall back to reasonable estimates (fixed char width of 8, string-length-based width, and fontSizePoints * dpi / 72 for height).

Test corrections

• TestSecondsRoundingWithoutMilliseconds: expect "02:34:08" (was "02:34:07")
• TestBug60031: expect "09:54:34" for 903 ms value (was "09:54:33")
• TestNPOI1469: truncate DateTime.UtcNow to whole seconds before writing cells, so DateTime.ToString (truncates ms) and DataFormatter (rounds ms) agree

• Fixes ExcelStyleDateFormatter incorrect Format result #863

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