fix: use canonical shipping destination address fields

[FanouZeng-TT]

Description

ShippingDestination inherits the canonical address fields
address_locality and address_region. The conformance helpers instead passed
locality and region when creating destinations:

ShippingDestination(
    ...,
    locality=dest_data.get("locality", dest_data.get("city")),
    region=dest_data.get("region", dest_data.get("state")),
)

The model accepts extra fields, so those names are serialized as non-contract
keys while address_locality and address_region remain unset. The same
mismatch appears in the checkout-update lifecycle destination.

Fix: pass the canonical address field names in both construction paths.

A direct serialization regression confirms that the old keys omit the canonical
fields, while the corrected fields serialize exclusively as
address_locality and address_region.

Type of change

• Bug fix (non-breaking change which fixes an issue)

---

Is this a Breaking Change or Removal?

N/A — fixes conformance test request construction without removing schema fields.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have run a direct serialization regression that proves the fix
• New and existing integration tests pass locally (requires a configured merchant server)
• Any dependent changes have been merged and published in downstream modules

[vishkaty]

Ran this branch against the reference with the python sdk at head: the 52 suite errors persist, because both construction sites still build shipping_destination.ShippingDestination while the post #83 destination unions accept only the request variants, so validation rejects the instance with a model_type error before the renamed fields are reached. On top of this branch, switching create_checkout_payload in integration_test_utils.py to ShippingDestinationCreateRequest and the test_update_checkout site in checkout_lifecycle_test.py to ShippingDestinationUpdateRequest takes the suite from 52 errors to 2. The remaining 2 are the OrderTest failures already red in the nightly since Aug 21, a server side Payment validation error in the reference, unrelated to these fields.

[FanouZeng-TT]

Thanks for testing this against the SDK at head. I updated both construction sites to use the request-specific models: ShippingDestinationCreateRequest for checkout creation and ShippingDestinationUpdateRequest for checkout updates. I also reproduced the model_type failure with the generic model and verified both request variants against the post-#83 destination unions, then reran Ruff, formatting, full pre-commit, Python compilation, and git diff --check.

[FanouZeng-TT]

Rebased this branch onto the latest main and resolved the merge conflict. The request-specific ShippingDestinationCreateRequest / ShippingDestinationUpdateRequest updates are now already present on main, so the remaining diff is limited to the canonical address_locality / address_region field-name fix.

Local verification:

• python3 -m py_compile checkout_lifecycle_test.py integration_test_utils.py
• uv run --no-sync ruff check checkout_lifecycle_test.py integration_test_utils.py
• uv run --no-sync ruff format --check checkout_lifecycle_test.py integration_test_utils.py
• uv run --no-sources request-model construction check against the published SDK
• uvx pre-commit run --all-files
• git diff --check

[FanouZeng-TT]

Updated this PR to also normalize the fixture destination in get_test_destination(). A test_destination configured with the standard field names (address_locality/address_region) now reaches the request intact, while legacy locality/city and region/state keys still populate the standard names.

This closes the gap reported in #116: previously a destination configured with standard field names was silently replaced by the default locality. Verified offline against create_checkout_payload() — fail-before produced address_locality='San Francisco' / address_region=None, pass-after carries the configured values.