Capitalize first letter efficiently.

CapitalizeFirstLetter.cs

public static string? CapitalizeFirstLetter(this string? text)
{
    if (string.IsNullOrWhiteSpace(text)) return text;

    StringBuilder result = new(text);

    var length = text!.Length;
    for (var i = 0; i < length; i++)
    {
        var c = text[i];

        if (!char.IsLetter(c))
            continue;

        result[i] = char.ToUpper(c);
        break;
    }

    return result.ToString();
}