[Chore] Replace the multi-group Measure row merger with a batch merger

## Summary

Merge vectorized Measure results without first converting them into individual `InternalDataPoint` objects. Follow-up to #14066 under #13998.

## Size audit and dependencies

Classification: **tracking parent**, not an executable leaf or automated implementation task.
Boundary: the production multi-group Measure caller of `MergeGroupMIterators` and its `sortableDataPoints` / `sortedMIterator` stack.
This spans batch consumption, caller/egress migration, schema alignment, ordering/version deduplication, and resource ownership. Decompose after the legacy removal merges.
Blocked by: #14066 via BanyanDB PR apache/skywalking-banyandb#1326.

## Requirements

R1. Consume and merge per-group batches directly; do not reconstruct the row merger internally.
R2. Preserve requested ordering, version-based deduplication, schema alignment, and pagination.
R3. Materialize protobuf only where the response boundary requires it; preserve tracing and response compatibility.
R4. Release consumed batches correctly on completion, cancellation, and errors.

## Concrete oracle

Two groups supply these records, with duplicate versions split across batches:

```text
timestamp=10, SID=7, version=1, value=100
timestamp=10, SID=7, version=3, value=300
timestamp=20, SID=8, version=1, value=200
```

Ascending output is `(10,7,3,300)` followed by `(20,8,1,200)`. Descending reverses that order. Ascending with offset 1 and limit 1 returns only `(20,8,1,200)`.

## Completion criteria and RED-test direction

- [ ] The real processor multi-group caller consumes the batch-native merger.
- [ ] Tests assert the exact oracle across batch boundaries, plus index ordering and supported schema alignment.
- [ ] A path-sensitive production-caller regression fails if row iteration/materialization is restored. Output assertions alone are insufficient: the existing merger already produces these answers.
- [ ] Each executable child identifies its public boundary and failing test before implementation; no helper-only foundation PR counts as completion.
- [ ] Cancellation/error tests verify resource release; benchmark comparisons report allocations without claiming a new resource bound that has not been proved.

Packages: `banyand/query`, `pkg/query/logical/measure`, `pkg/query/vectorized/measure`.

```sh
go test ./banyand/query ./pkg/query/logical/measure ./pkg/query/vectorized/measure/...
go test ./test/integration/standalone/query/... ./test/integration/distributed/query/...
```

## Out of scope

Changing ordinary Top or GroupBy semantics; the internal TopN pre-aggregation RPC; schema-evolved aggregate partial reduction (separate workstream).

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.

Start with the production multi-group Measure caller of MergeGroupMIterators and the sortableDataPoints/sortedMIterator stack in banyand/query, pkg/query/logical/measure, and pkg/query/vectorized/measure. Run the listed Go tests and inspect the RED-test direction before implementation. Done means the caller uses the batch-native merger, preserves ordering, deduplication, schema alignment, and pagination, and tests cover boundaries, cancellation, errors, and resource release.

Written by the indexing model from the issue text.