Add support for array and List<T> properties in CSV parsing

[Copilot]

Enables parsing comma-delimited values within a CSV column into arrays or List<T> properties.

Changes

Property parsing

• Added CsvPropertyKind.List to distinguish collection properties
• Extended CsvPropertyDefinition with element type metadata (type name, kind, date format, delimiter)
• Modified Parser.cs to detect and validate array types and List<T> generics

Code generation

• Added ParseListToArray<T> and ParseListToList<T> helper methods to generated code
• Split column values by delimiter and parse each element according to its type
• Support all existing element types: primitives, enums, dates, ISpanParsable<T>

Element types
List elements support the same types as scalar properties:

• Strings, enums, primitives implementing ISpanParsable<T>
• Date/time types with [CsvDateFormat] attribute

Example

public partial class Product
{
    [CsvHeaderName("Tags")]
    public string[]? Tags { get; set; }

    [CsvHeaderName("Prices")]
    public List<decimal>? Prices { get; set; }

    [GenerateCsvParser(IncludeProperties = true)]
    public static partial IEnumerable<Product> Parse(SepReader reader);
}

CSV input:

Tags,Prices
gadget,tool,hardware,9.99,19.99,29.99
electronics,14.99,24.99

Result: Tags parsed as string[], Prices as List<decimal>.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Consider adding support for list-like types for properties</issue_title>
<issue_description>Like arrays or List<T>.</issue_description>

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

• Fixes Consider adding support for list-like types for properties #6

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[AustinWise]

Ideally I'd like the generated code to put the helpers into a file-scoped class instead of duplicating them into each instance. Or add a assembly to the Nuget that contains the attributes and the helpers.

But I don't actually need this feature right now, so I'm not going to work on this more.