Move customerNumber from request root into each consignment's product

[crakter]

Summary

Bring's Booking API expects customerNumber inside consignments[].product.customerNumber, but the SDK was emitting it at the request root. Bring's gateway reads from the product slot, finds nothing, and rejects every consignment with BOOK-INPUT-019 "Customer number must be provided". The BookingRequest constructor invariant (non-empty customerNumber) prevented a local failure but couldn't help the wire shape — every live booking would fail.

This was masked because the existing BookingApiTest only validated the (incorrect) root placement against a mock client.

Change

• BookingRequest::toArray() no longer emits customerNumber at the root. Instead, it injects the field into each consignment's product object at serialization time.
• The public SDK shape is unchanged: callers still pass customerNumber once on BookingRequest. The repetition Bring's schema demands per consignment is an implementation detail.
• Test updated to pin the field at consignments[0].product.customerNumber AND to assert it is NOT present at the root, locking in the correct shape against the live API.

Confirmed against https://developer.bring.com/api/booking/ — the schema lists customerNumber as a required property of the product object inside each consignment.

Test plan

• vendor/bin/phpunit — 198 tests, all green
• vendor/bin/phpstan analyse — no errors
• BookingApiTest now asserts the field at the product level and explicitly forbids the root placement

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Generated by Claude Code

[gemini-code-assist]

Code Review

This pull request updates the serialization of BookingRequest to nest the customerNumber inside each consignment's product object rather than placing it at the request root, aligning with the expectations of Bring's Booking API. The corresponding unit tests have been updated to reflect this structural change. Feedback was provided to replace the array union operator (+) with direct array assignment to improve readability and prevent potential confusion regarding array merging behavior in PHP.

[gemini-code-assist]

Using the array union operator (+) for merging arrays can be non-intuitive in PHP because the left-hand side takes precedence (unlike array_merge where the right-hand side overwrites). To improve readability and avoid potential confusion for future maintainers, it is more idiomatic to use direct array assignment.

                $product = (array) $arr['product'];
                $product['customerNumber'] = $customerNumber;
                $arr['product'] = $product;