[Enhancement] Add traffic size distribution per requestCode in RemotingCodeDistributionHandler

### Before Creating the Enhancement Request

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

### Summary

`RemotingCodeDistributionHandler` currently tracks the request count per requestCode, but does not record how many bytes each requestCode consumes. This makes it hard to identify which commands are responsible for high network traffic.

### Motivation

In production, it is common to have many requestCodes active at the same time. Count alone cannot tell us which command is a traffic hotspot. Adding per-requestCode traffic size distribution allows operators to quickly pinpoint bandwidth-heavy commands without relying on external packet capture tools.

### Describe the Solution You'd Like

- Introduce `TrafficStats` (a pair of `LongAdder` for count and trafficSize) to replace four separate `ConcurrentHashMap`s with two.
- Add `calcCommandSize()` that always includes a fixed protocol overhead (29 bytes) plus body length — O(1), zero iteration cost on the hot path.
- Add `enableDetailedTrafficSize` flag in `NettyServerConfig`. When enabled, remark and extFields variable-length bytes are also counted (O(n) path). The flag can be toggled at runtime via `updateBrokerConfig`.
- Log inbound/outbound traffic snapshots in `NettyRemotingServer.printRemotingCodeDistribution()` alongside existing count snapshots.

### Describe Alternatives You've Considered

Iterating over extFields on every message was considered but rejected as the default path due to O(n) cost on the hot path. It is kept as an opt-in mode behind the switch.

### Additional Context

_No response_

Start with RemotingCodeDistributionHandler, NettyServerConfig, and NettyRemotingServer.printRemotingCodeDistribution(). Trace the existing requestCode count maps, configuration update path, and inbound/outbound snapshot logging. Done means traffic sizes are reported per requestCode, detailed counting is runtime-toggleable, and the default path avoids extFields iteration.

Written by the indexing model from the issue text.