fix: restore Python SDK compatibility for conformance and samples#17

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adrianmcphee wants to merge 3 commits intoUniversal-Commerce-Protocol:mainfrom

adrianmcphee:main

Commits on Mar 3, 2026

fix(schemas): define base entities before dependents and freeze key root models
adrianmcphee
committed
fix(discovery): support legacy and keyed discovery payloads in pydantic v2
adrianmcphee
committed
fix(compat): restore legacy shopping request/response module aliases
adrianmcphee
committed