feat(promql): preserve and plan topk over sum_over_time/count_over_time (ASAPQuery #706 parity)

[zzylol]

Summary

Add semantic planning parity with ProjectASAP/ASAPQuery#706 for Top-K over sum_over_time and count_over_time.

Reproduction

Both queries lower successfully through frontend-promql, but the normal summary-selection path used by ASAPQuery-backend currently produces no legal summary candidate for at least the value-ranked case:

topk(5, sum_over_time(m[1m]))
topk by (job) (5, count_over_time(m[1m]))

ASAPQuery #706 defines an important semantic distinction:

• topk(sum_over_time(...)) ranks each series by the sum of sample values (value-weighted heap);
• topk(count_over_time(...)) ranks each series by the number of samples (count-weighted heap).

The current AggIntent::TopK / SketchQuery::TopK representation carries k but does not carry the ranking/weighting basis, so downstream physical compilation cannot preserve this distinction without re-parsing PromQL.

Scope

• Represent the Top-K ranking basis in canonical pre-ASAP and post-ASAP IR using language-neutral semantics.
• Lower the two #706 query shapes to distinct semantic plans.
• Generate legal heap-bearing summary candidates for both nested temporal cases.
• Preserve by(...) grouping separately from the in-summary item key.
• Reject non-collapsible shapes (topk(rate(...)), topk(avg_over_time(...)), etc.) rather than silently selecting a wrong summary.
• Keep SQL/other frontends source-compatible by requiring them to choose the appropriate ranking basis explicitly.

Acceptance criteria

• PromQL lowering tests pin the distinct ranking basis for both queries.
• ASAP-aware mapping tests produce heap-bearing candidates with count vs value update semantics.
• End-to-end planner tests cover grouped and ungrouped forms plus negative non-collapsible cases.
• Serialized IR round-trips without dropping the ranking basis.

Downstream execution tracking: ProjectASAP/ASAPQuery-backend#502.
Parent compatibility audit: ProjectASAP/ASAPQuery-backend#501.