#### Description of the issue/feature this PR addresses:
Apple Pay (and Google Pay) express checkout via Stripe fails on the cart page with an "update postal address" error when a Starshipit delivery carrier is configured, while normal checkout with a full address works fine. No request even reaches Starshipit's own API logs, because the request is rejected on Odoo's side.

#### Current behavior before PR:
Express checkout wallets only disclose a partial shipping address before the payment is authorized (city, zip, state, country) — the street is withheld by the wallet for privacy. website_sale rates the delivery carriers against this partial address, setting the express_checkout_partial_delivery_address context key so connectors only require the fields available at that stage. The UPS/USPS/DHL/bpost connectors honor this key and skip the street requirement, but delivery_starshipit ignores it: Starshipit._rate_shipment always sends the (empty) destination street to the /api/rates endpoint, which requires it and returns success:false with "street parameter value is required". _starshipit_send_request raises this as a UserError, which propagates out of starshipit_rate_shipment and aborts the entire express checkout rating RPC (_get_delivery_methods_express_checkout), so no carrier at all is returned to the wallet — hence the endless "update postal address" prompt.

#### Desired behavior after PR is merged:
During express checkout, Starshipit is skipped when the partial address has no street (it returns an unsuccessful rate without calling the API), so the other published carriers are still rated and the wallet shows the available shipping options. Starshipit is rated normally at the regular checkout step once the full address is known. Normal (non-express) checkout is unchanged.

opw-6393393