Feature Add positions DTOs and enhance invoicing

[kaspernowak]

This PR introduces complete support for creating and sending invoices using structured DTOs, including all supported Bexio position types.

✅ What’s Included

• New DTOs for all invoice position types:
  • AddDefaultPositionDTO
  • AddTextPositionDTO
  • ...and others under src/Dto/*
• New request classes:
  • CreateAnInvoiceRequestNew
  • EditAnInvoiceRequestNew
  • SendAnInvoiceRequest
  • MarkAnInvoiceAsSentRequest
  • ...and Create, Edit, Delete, Fetch, and FetchList requests for all position types
• New test coverage for the above requests and DTOs
• Support for sending and marking invoices as sent via SendInvoiceDTO

💡 Usage Example

$invoiceDto = new CreateInvoiceDTO(
    title: 'Test',
    contact_id: $contacts->first()->id,
    // ...
    positions: [
        new AddTextPositionDTO(
            type: 'KbPositionText',
            text: (string) Str::uuid(),
            show_pos_nr: true
        ),
        new AddDefaultPositionDTO(
            type: 'KbPositionCustom',
            amount: 1,
            unit_id: $units->first()->id,
            account_id: 145,
            tax_id: $taxes->first()->id,
            text: Str::uuid(),
            unit_price: 100,
        ),
    ],
);

$invoice = $connector->send(new CreateAnInvoiceRequestNew(invoice: $invoiceDto))->dto();

$send = $connector->send(new SendAnInvoiceRequest(...));
$markAsSent = $connector->send(new MarkAnInvoiceAsSentRequest(...));

⚠️ Compatibility Note

The existing CreateAnInvoiceRequest class appears to be incompatible with the documented example due to a type mismatch in the filterPositions() method:

Argument #1 ($positions) must be of type Collection, array given

To avoid breaking changes, I've added new request classes (CreateAnInvoiceRequestNew, etc.) that work with the new DTO structure.
We may want to decide whether to:

• Fix and maintain the old request for compatibility
• Or deprecate it and focus solely on the updated approach

closes #7

[StanBarrows]

@kaspernowak
We’ve just completed the OAuth PR and will take a closer look at this in the coming weeks.

[kaspernowak]

@StanBarrows Thank you! Looking forward to it. I think this would have higher prio than #34, as the structured addresses won't really be required before December.