refactor: fold heap-CMS count_events into aggregation_sub_type - #719

…_type (#670)

CountMinSketchWithHeap previously split its SUM/COUNT weighting across two
places: aggregation_sub_type (fixed to the now-redundant "topk") and a
separate parameters["count_events"] boolean, duplicating and diverging from
how plain CountMinSketch/MultipleSum already encode the same axis via
sub_type alone. Hard-cutover to aggregation_sub_type: "sum"|"count" for all
three CMS-family types, removing count_events entirely.

Introduces asap_types::aggregation_mode (AggregationMode/CountMode/
MinMaxMode) as the single typed seam AggregationConfig::mode() exposes;
capability_matching's three separate weighting-compatibility functions and
accumulator_factory's duplicate sub_type parsers now route through it
instead of each re-deriving the same semantics.

The planner (promql.rs, sql.rs) patches a topk candidate's sub_type to the
detected weighting right after building it, since map_statistic_to_
precompute_operator's placeholder "topk" sub_type is only a stand-in until
the real weighting is known; candidate_gen.rs/atomic_costs.rs updated to
match. Backward-compat: none needed, AggregationConfig is regenerated by
the planner per query rather than persisted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K2SLcSk9UnZi5iAWKt26kH

…b_type change

The Arroyo pipeline generator derives its UDF name as
f"{aggregationType}_{aggregationSubType}", and the topk-vs-non-topk column
selection patch keyed off aggregationSubType == "topk". Both broke once
CountMinSketchWithHeap's sub_type moved to "sum"/"count" (2e950f5, #670):
UDF lookup would 404 on the missing countminsketchwithheap_sum/_count
templates, and the column-selection patch would silently stop firing.

Renames the existing (COUNT-semantics) UDF template/function to
countminsketchwithheap_count, and switches the column-selection check to
aggregationType, which uniquely identifies a topk config regardless of its
subtype. A value-weighted (SUM) Arroyo UDF was never implemented -- the old
single template always used count semantics regardless of weighting -- so
countminsketchwithheap_sum intentionally has no template yet; that case now
fails loudly with a clear "template not found" error instead of silently
returning wrong (count-weighted) results, which is what actually happened
before this change.

Roborev: closes review 205.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Completes ae9c593 (the file rename alone accidentally landed as its own
commit): renames the UDF fn inside the template to match, switches the
topk column-selection patch from aggregationSubType == "topk" to
aggregationType == "countminsketchwithheap", and adds a regression test
covering both new sub_type values.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>