feat(planner/elastic): explore whether data_ingestion_interval_ms should be used in ElasticSingleQueryProcessor #448

Background

ElasticSingleQueryProcessor stores data_ingestion_interval_ms (renamed from data_ingestion_interval in #427) but never uses it — it only uses t_repeat_ms for window sizing and cleanup. The field is currently marked #[allow(dead_code)].

Work

Investigate whether data_ingestion_interval_ms should influence the Elastic plan (e.g. window sizing for spatial-style queries, validation, or the repetition_delay_ms % data_ingestion_interval_ms == 0 check that already exists in generate_elastic_plan). If it should be used, wire it in and add tests. If not, remove the field.