American spelling in two comments (#138)

## Summary

American spelling in two comments (serialize), from a workspace-wide
sweep for British forms. The receipt's fulfillment status values stay as
the wire contract spells them. Nothing published changes and no release
is cut for it.

Worked with: Varun.

## Type of change

- [ ] Bug fix (no breaking change)
- [ ] New feature (no breaking change)
- [ ] Breaking change (existing callers must update)
- [x] Docs, tests, or internal maintenance only

## Public API

none

## Test plan

`ruff check`, `ruff format --check`, `pytest tests/` locally.

## Checklist

- [x] Tests cover the new behavior, and the suite passes locally
- [x] Lint, format, and type checks pass
- [x] Docs and README examples updated if the public surface changed
- [x] No secrets, credentials, or personal data in the diff or the tests

Author: vvillait88

agentscore_commerce/challenge/body.py

@@ -102,7 +102,7 @@ def build_402_body(
     if agent_memory is not None:
         # AgentMemoryHint is a dataclass; merchants pass it directly via
         # first_encounter_agent_memory(...). Convert here so JSONResponse /
-        # json.dumps can serialise without per-merchant boilerplate.
+        # json.dumps can serialize without per-merchant boilerplate.
         body["agent_memory"] = (
             asdict(agent_memory) if is_dataclass(agent_memory) and not isinstance(agent_memory, type) else agent_memory
         )

tests/test_checkout.py

@@ -331,7 +331,7 @@ class _Verified:
 
     async def settle_payment(self, _payload: Any, _requirement: Any) -> Any:
         # ProcessX402Settle treats a falsy success as a settle_failed phase via the
-        # exception raised by settle_result_to_json_bytes when it tries to serialise
+        # exception raised by settle_result_to_json_bytes when it tries to serialize
         # an empty dict, so we shape the response as a plain JSON-serializable dict.
         if not self.settle_success:
             raise RuntimeError("settle rejected")