fix(feedback): serialize and validate legacy feedback

[routeplane-ops]

Summary

Closes #9.

• Preserve request_id/score and None return; send trace_id and integer value to the existing legacy endpoint.
• Accept integral int/float scores from -10 through 10 without rescaling. Reject fractional, out-of-range, boolean, non-numeric and nonfinite input before HTTP dispatch.
• Omit absent/null/empty comments; explicitly reject all nonempty comments, including whitespace. Preserve the synchronous REST helper on both Routeplane and AsyncRouteplane.
• Document the correction and add an unreleased changelog entry. No new service, named feedback, target lookup, durability, package publication or version bump.

Validation

• New regression test fails against the previous wire format (request_id/score rather than trace_id/value).
• 273 targeted feedback/resource tests pass; full suite: 302 passed.
• Ruff lint and format checks pass; mypy passes all 21 source files; git diff --check passes.
• Parameterized direct-resource, sync-client and async-client paths verify exact wire body and integer JSON type, no-dispatch validation failures, return values and HTTP errors.
• Hosted Python 3.9–3.13 and lint gates must pass before protected merge. Published-package inference-to-feedback acceptance against both editions remains pending; this source PR alone is not delivered-artifact evidence.

Scope: approved A1 correctness repair described by #9. No merge or publication requested by this PR creation.

[routeplane-ops]

Validation update at 9ee17e0: the initial CI run 34000638102 retained four existing metadata-fixture failures because OpenAI 3.8.0 defaults to httpx2 while respx mocks httpx. The four metadata tests now explicitly inject supported httpx sync/async clients, preserving assertions and cleanup; production transport and dependency declarations are unchanged. OpenAI 3.8.0 installed source explicitly accepts both httpx and httpx2 clients. A clean current-dependency environment now passes all 302 tests, Ruff lint/format and mypy. Hosted matrix rerun remains the merge gate; no release or delivered-version runtime claim.