[Bug] Support schema-evolved multi-group Measure aggregation

[hanahmily]

Summary

Make valid aggregate queries succeed when participating storage groups have different projected schemas. Follow-up to #14066 under #13998.

Size audit and dependencies

Classification: tracking parent, not an executable leaf or automated implementation task.
Boundary: multi-group DistributedPlan.Execute through executeAgg, ReduceRawFrames, and ReducePartialBatches.
Schema alignment and storage-group-aware replica handling are independently testable changes; split them into executable tasks before implementation.
Blocked by: #14066 via BanyanDB PR apache/skywalking-banyandb#1326, to finalize the remaining boundary after legacy removal.

Proposed initial slice

Normalize missing projected, non-grouping tags to null before partial reduction, rather than rejecting the query because partial layouts differ. Do not simply disable structural schema validation.

Concrete oracle

• Old schema: svc,value; rows (old,2) and (old,3).
• New schema: svc,zone,value; rows (new,west,7) and (new,west,11).
• Query: GROUP BY svc, SUM(value), project svc,zone.

Expected unordered output:

old, NULL, 5
new, west, 18

Different service keys deliberately avoid ambiguity over representative values of non-grouping tags. Currently differently shaped partial batches can fail with partial ... schema mismatch.

Completion criteria

• The schema-evolution oracle succeeds through the distributed production caller, not only a reducer helper; add a regression that fails on the current structural mismatch.
• Normalization preserves aggregate-state columns, including count sidecars used by MEAN, and rejects genuinely incompatible types with a clear error.
• Replica deduplication preserves storage-group provenance: contributions 5 and 18 for service api from two different storage groups must total 23, even when both groups use shard 0; duplicate replicas of either contribution must not increase that sum. This requires its own focused implementation/test slice.
• Each executable child activates the real distributed caller and has independently specified expected results.

Relevant code: pkg/query/vectorized/measure/reduce.go, pkg/query/vectorized/measure/plan/distributed.go; extend distributed-plan and topology-matrix coverage.

go test ./pkg/query/vectorized/measure/...
go test ./test/integration/distributed/query/...

Out of scope of the first slice

Missing GroupBy keys: these fail earlier during planning and need a separately specified change, not an assumed reducer-only fix. Also exclude changing aggregate/operator semantics or replacing the ordinary multi-group row merger.

Parent: #13998.

Compatibility and review policy

• Preserve existing on-disk and wire formats and mixed-version compatibility. Any necessary protocol change requires a separately reviewed compatibility contract.
• Use explicit, hand-calculated expected results; do not depend on the removed row engine as the test oracle.
• Human review enforces the no-new-row-path policy. A row-call-site lint guard is not required.