Applications that display an in-progress review currently need to duplicate the SDK's polling loop to keep their UI or CI log updated. Add an optional on_update callback to both clients' wait_for_review methods so callers can observe each validated poll, including terminal states, while retaining the existing backoff and request count.

The async client supports synchronous and awaitable callbacks. Callbacks run inline, count toward the existing deadline, and propagate exceptions; the deadline context is restored on failure. Existing callers remain unchanged.

Validation:

• Nine new HTTP integration cases pass, covering both clients, async callback ordering, no extra requests, callback failures, deadline handling and invalid review IDs.
• Ruff lint/format, mypy, operation/outcome contracts and wheel/sdist builds pass.
• Full suite: 148 passed, one existing Windows HTTP deadline case failed once; that exact case passed on isolated rerun.
• Generation check reports an existing difference in customer_review_detail.py; this PR does not change the schema, templates or generated files.

Prepared with AI coding assistance as an application contribution. Documentation explains callback semantics and includes a usage example.