[Merchant API - Product] Missing fields in Shipping type

[Alexis12987]

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Summary of the issue

Context
The type Shipping (belong in /shopping/merchant_products_v1/types/products_common.py) have two missing fields (handling_cutoff_time & handling_cutoff_timezone) compared to Google Merchant API documentation & Google discovery document
Google Merchant Product discovery document : https://merchantapi.googleapis.com/$discovery/rest?version=products_v1
Google Merchant API documentation : https://developers.google.com/merchant/api/reference/rpc/google.shopping.merchant.products.v1#shipping

Expected Behavior:
No error raised when one of those two field is specified to update/insert a product

Actual Behavior:
We can't specify those two fields when a ProductInput is required in a request, for example insert/update product. A ValueError is raised :
ValueError: Unknown field for Shipping: handling_cutoff_timezone

API client name and version

google-shopping-merchant-products = 1.3.0

Reproduction steps: code

from google.shopping import (
    merchant_products_v1,
)

credentials = "MY_CREDENTIALS"
datasource = "my_datasource"
product = {
    "content_language": "fr",
    "offer_id": "9628548530525",
    "feed_label": "test",
    "product_attributes": {
        "price": {"currency_code": "EUR", "amount_micros": "1000000"},
        "shipping_height": {"unit": "cm", "value": 55.0},
        "image_link": "https://www.example.com/image.jpg",
        "shipping": [
            {
                "postal_code": "44200",
                "region": "fr",
                "price": {"currency_code": "EUR", "amount_micros": "4000000"},
                "handling_cutoff_timezone": "5",
                "max_transit_time": "5",
                "min_handling_time": "2",
                "min_transit_time": "5",
                "country": "fr",
            }
        ],
        "availability": "IN_STOCK",
        "product_width": {"value": 4.0, "unit": "cm"},
        "product_height": {"value": 5.0, "unit": "cm"},
        "title": "title",
        "gtins": ["3234567890126"],
        "product_length": {"value": 55.0, "unit": "cm"},
        "description": "description",
        "product_weight": {"unit": "kg", "value": 55.0},
        "link": "https://www.example.com/product1",
    },
    "name": "accounts/124659270/productInputs/ZnJ-dGVzdH45NjI4NTQ4NTMwNTI1",
}

client = merchant_products_v1.ProductInputsServiceClient(
    credentials=credentials,
)

result = client.update_product_input(
    request=merchant_products_v1.UpdateProductInputRequest(
        product_input=merchant_products_v1.ProductInput(product),
        data_source=datasource,
    )
)

Reproduction steps: supporting files

No response

Reproduction steps: actual results

Reproduction steps: expected results

No response

OS & version + platform

Ubuntu 24.04.3 LTS

Python environment

3.10.19

Python dependencies

No response

Additional context

No response