[Enhancement] Reduce pull/dispatch path allocation via primitive arrays, ThreadLocal reuse, and lambda elimination

### Before Creating the Enhancement Request

- [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature.

### Summary

Reduce allocation in the pull/dispatch path by replacing boxed collections with primitive arrays, reusing DispatchRequest via ThreadLocal, merging mapped file slices, and eliminating CompletableFuture callback lambdas.

### Motivation

JFR profiling on the broker pull/dispatch path reveals several per-message allocation hotspots:

1. **`GetMessageResult`** — stored message offsets as `List`, boxing every `long` into a `Long` object. Under high pull QPS, this creates thousands of short-lived `Long` objects and `ArrayList` resize overhead per second.

2. **`DispatchRequest`** — a new `DispatchRequest` object is created for every message dispatched to ConsumeQueue/IndexService/TimerWheel. The object has mutable fields that could be reset and reused via ThreadLocal.

3. **`DefaultMappedFile.selectMappedBuffer`** — creates two separate `ByteBuffer` slices for position+size, then wraps them. Can be merged into a single slice operation.

4. **`DefaultMessageStore.putMessage/putMessages`** — wraps `asyncPutMessage` result in a `thenAccept` lambda callback for stats logging. The lambda captures `this` and `beginTime`, creating a closure object per message.

### Describe the Solution You'd Like

1. `GetMessageResult`: replace `List` with `long[]` + add `addQueueOffset(long)` method. Right-size initial capacity with constructor parameter.
2. `DispatchRequest`: change `final` fields to mutable + add `reset()` method for ThreadLocal reuse.
3. `DefaultMappedFile`: merge dual-slice into single `selectMappedBuffer` operation with cached append slice.
4. `DefaultMessageStore`: remove `thenAccept` callback, inline stats logging into `CommitLog` or caller.
5. `ConsumeQueue`: make `topicQueueKey` a `final` field to avoid per-call computation.

### Describe Alternatives You've Considered

- Use `LongAdder` instead of `long[]` for offsets — not applicable, offsets need ordering.
- Keep `thenAccept` callback but use a static method reference — still captures `this`, doesn't eliminate allocation.
- Use object pool instead of ThreadLocal for DispatchRequest — ThreadLocal is simpler and sufficient for single-threaded dispatch.

### Additional Context

Part of a larger JFR-driven optimization effort. Related PRs: #10443, #10444, #10514, #10524.

Start by reviewing GetMessageResult, DispatchRequest, DefaultMappedFile, DefaultMessageStore, and ConsumeQueue, along with related PRs #10443, #10444, #10514, and #10524. Use the JFR allocation hotspots in the issue as the guide. Done means the requested allocation reductions are implemented across the pull/dispatch path without changing message behavior.

Written by the indexing model from the issue text.