Capability-matching fallback never matches keyed aggregations (grouping_labels = []) #779

Problem

The query engine's capability-matching fallback (asap_types::capability_matching::find_compatible_aggregation, used when a query has no entry in the inference config) never matches keyed aggregations.

labels_compatible requires config.grouping_labels == requirements.grouping_labels. Both planners deliberately set grouping_labels = [] for keyed types and put the output labels in aggregated_labels instead (planner/labels.rs::set_subpopulation_labels; MultipleSum/MultipleMinMax/MultipleIncrease, CountMinSketch, CountMinSketchWithHeap, HydraKLL). So for any grouped query such as sum by (svc) (x) served by a keyed config, the fallback finds no value candidate and the query goes to Prometheus.

The primary path, explicit query-config references (SimpleEngine::find_query_config → get_aggregation_id_info), is unaffected, so this only bites when the inference config lacks the query (ad-hoc queries, or configs served without an inference config).

Pre-existing: labels_compatible and set_subpopulation_labels are unchanged on main. Found while adding key-aggregation deployment to the optimizer (#756).

Repro

Deploy the pair the legacy planner produces for sum by (svc) (x) with CMS (grouping_labels = [], aggregated_labels = [svc], plus the paired DeltaSet), then call find_compatible_aggregation with that query's requirements: it returns Ok(None).

Fix direction

For keyed value types, compare the requirement's output labels against grouping_labels ∪ aggregated_labels (the full key), not grouping_labels alone. Add a regression test using the legacy planner's split.