Convert NieuwbouwOffice to a Saloon connector

[jhhazelaar]

Summary

• Add saloonphp/saloon as a runtime dependency
• Turn NieuwbouwOffice into a Saloon\Http\Connector with sensible defaults
• Replace the placeholder example test with focused connector tests

Details

• NieuwbouwOffice now extends Saloon\Http\Connector and uses the AcceptsJson and AlwaysThrowOnErrors plugins.
• Constructor takes a required $token and an optional $baseUrl (defaults to https://api.nbo.nl/rest) so staging/test environments can override it.
• defaultAuth() returns a TokenAuthenticator with the apikey prefix, so requests are sent with Authorization: apikey <token> instead of Bearer <token>.

Tests

• Asserts the connector extends Saloon's Connector.
• Asserts the default base URL and that it is overridable via the constructor.
• Asserts the authenticator type, token, and prefix.
• Asserts outgoing requests carry the Authorization: apikey <token> and Accept: application/json headers via createPendingRequest().

All 7 tests pass locally with vendor/bin/pest.