nationex: normalize additional tracking statuses

[HansDaigle]

Summary

• expand Nationex status normalization to cover additional shipment states returned by the carrier
• map Creation/DataReceived to pending instead of defaulting to in_transit
• add mappings for partial, pickup, cancellation, and return statuses
• fallback unknown carrier states to unknown
• add test coverage for all mapped Nationex statuses

Why

Nationex returns statuses like Creation, DataReceived, OutForPickup, ReturnCompleted, and partial status variants. Without explicit mappings these can be normalized incorrectly (for example as in_transit).

Validation

• /Users/hansdaigle/git/tandem-monorepo/.venv/bin/python -m pytest -q plugins/nationex/tests/nationex/test_tracking.py

[HansDaigle]

Recommendation for tracking normalization work: prefer when querying carrier tracking APIs (including via Karrio). We verified localized descriptions (e.g., FR) can vary in wording, while the normalized status remains stable; using English reduces parser drift and keeps mappings deterministic across carriers.

[HansDaigle]

Tracking note/TODO: Nationex POD images are returned as base64 payloads (not URL refs). We intentionally removed image-fetching for now to avoid persisting large blobs in tracking payload/storage. Follow-up: decode base64, upload to object storage (S3/R2/etc), and persist only generated URLs.