Fix phone number format: escaped dashes misidentified as grouping chars; decimal cast in special format classes

[Copilot]

DataFormatter incorrectly formats phone numbers like ###\-###\-#### as 1-234-56-7-890 instead of 123-456-7890, and SSNFormat/ZipPlusFourFormat/PhoneFormat throw InvalidCastException when FormatRawCellContents passes a decimal value.

Changes

• DataFormatter.cs — alternate grouping detection: Run alternateGrouping.Match() against the original format string (before cleanFormatForNumber strips backslashes). After stripping, ###\-###\-#### becomes ###-###-#### and the regex incorrectly captures - as an alternate grouping separator. Matching on the raw string avoids this because the backslash breaks the [#0]{3} contiguity requirement.

• Format.cs — decimal cast fix: Replace (double)obj with Convert.ToDouble(obj, CultureInfo.InvariantCulture) in SSNFormat, ZipPlusFourFormat, and PhoneFormat, consistent with DecimalFormat. The direct cast throws when obj is a decimal, which is what FormatRawCellContents produces.

DataFormatter formatter = new DataFormatter(CultureInfo.GetCultureInfo("en-US"));

// Previously produced "1-234-56-7-890"
formatter.FormatRawCellContents(1234567890, -1, "###\\-###\\-####");  // → "123-456-7890"

// Previously threw InvalidCastException
formatter.FormatRawCellContents(1234567890, -1, "[<=9999999]###\\-####;\\(###\\)\\ ###\\-####");  // → "(123) 456-7890"

Original prompt

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This section details on the original issue you should resolve

<issue_title>Bug: NPOI does not format simple phone number format correctly</issue_title>
<issue_description>### NPOI Version
2.7.3

File Type

• XLSX
• XLS
• DOCX
• XLSM
• OTHER

Upload the Excel File

Not really needed, but here's a spreadsheet with 2 different phone number formats, one works and one doesn't: Formatting_Issue_Test.xls

Reproduce Steps

Use DataFormatter.FormatCellValue() or DataFormatter.FormatRawCellContents() to format a 10 digit numeric value with the following phone number format: "###-###-####" or "###\\-###\\-####" as Excel provides it.

Cell B3 in the uploaded example .xls file has an example of the issue.

Issue Description

When creating the number format for "###-###-####" the DataFormatter.CreateNumberFormat method incorrectly identifies this format string as using '-' as an alternate grouping character and updates the format accordingly. This leads to the final output looking like this: "1-234-56-7-890".

You can test this quickly by adding a test like this to TestDataFormatter.cs

[Test]
public void TestPhoneNumberFormat()
{
    DataFormatter formatter = new DataFormatter(CultureInfo.GetCultureInfo("en-US"));

    Assert.AreEqual("(123) 456-7890", formatter.FormatRawCellContents(1234567890, -1, "[<=9999999]###\\-####;\\(###\\)\\ ###\\-####"));
    Assert.AreEqual("123-456-7890", formatter.FormatRawCellContents(1234567890, -1, "###\\-###\\-####")); // returns 1-234-56-7-890
}

Note: This unit test also identifies a bug in DataFormatter.FormatRawCellContents when using SSNFormat, ZipPlusFourFormat, or PhoneFormat.

FormatRawCellContents converts the value to a decimal before calling Format:
result = numberFormat.Format(decimal.Parse(textValue));

But the Format methods of SSNFormat, ZipPlusFourFormat, and PhoneFormat all attempt to cast to a double, which throws an exception:
var result = ((double)obj).ToString(df, culture);

I updated these lines to use Convert.ToDouble the way DecimalFormat does in order to fix this:
var result = Convert.ToDouble(obj, CultureInfo.InvariantCulture).ToString(df, culture);</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes NPOI does not format simple phone number format correctly #1668

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