Add pagination support for list_namespaces

[vishnuprakaz]

Feature Request / Improvement

The REST catalog spec defines pageToken as a query parameter for GET /v1/{prefix}/namespaces, and next-page-token in the ListNamespacesResponse schema:

• https://github.com/apache/iceberg/blob/main/open-api/rest-catalog-open-api.yaml

Currently, RestCatalog.list_namespaces makes a single HTTP request and returns only the first page of results. If the server paginates the response, PyIceberg silently returns an incomplete namespace list.

This is the same gap that was fixed for list_views by @ebyhr in #3349 and is being fixed for list_tables in #3348.

The fix is to:

1. Add next_page_token field to ListNamespaceResponse
2. Loop through pages in list_namespaces using the same pattern as list_views

[vishnuprakaz]

I'd like to work on this.

[ebyhr]

@vishnuprakaz There is an existing PR #3347