feat: New zoned timestamp feature type (#6536) by nquinn408 · Pull Request #6537 · feast-dev/feast

Address Codex review findings on PR feast-dev#6537:

- Serialize ZonedTimestamp as an ISO 8601 string in feature_server_utils
  and proto_json so JSONResponse can encode zoned-timestamp features
  (the raw protobuf message is not JSON-serializable).
- Reject ZonedTimestamp as an Array/Set base type, since there is no
  ZONED_TIMESTAMP_LIST/_SET ValueType for to_value_type() to resolve.
- Preserve fixed-offset zones (e.g. UTC-07:00) on decode instead of
  silently falling back to UTC and shifting the wall-clock time.
- Resolve 'ZONED_TIMESTAMP' (and 'SCALAR_MAP') in
  _convert_value_type_str_to_value_type so registry REST/codegen no
  longer render the type as String.

Signed-off-by: Nick Quinn <nicholas_quinn@apple.com>