storage channel splitter for columns

[tbenr]

PR Description

Fixed Issue(s)

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

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Note

Introduces a dedicated query channel and splitter to isolate data column sidecar storage traffic from block/state operations and run queries asynchronously.

• Adds SidecarQueryChannel API and SidecarStorageChannelSplitter to route sidecar queries via an async runner while keeping updates synchronous
• Implements SidecarQueryChannel in ChainStorage
• Wires StorageService to publish/subscribe SidecarUpdateChannel and SidecarQueryChannel via the splitter
• Updates DataColumnSidecarDB to use SidecarQueryChannel instead of CombinedChainDataClient
• Updates BeaconChainController to create DataColumnSidecarDB using event channel publishers for SidecarQueryChannel and SidecarUpdateChannel

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[cursor]

Sidecar query parallelism significantly lower than established pattern

Medium Severity

The sidecar_storage_query AsyncRunner is created with parallelism of 1, while the existing storage_query AsyncRunner uses STORAGE_QUERY_CHANNEL_PARALLELISM which equals 20. This 20x reduction in parallelism could cause sidecar query operations to become a bottleneck during high-load scenarios like sync, backfill, or data availability sampling, where many concurrent queries are expected. The stated goal of isolating data column operations "under high load" may be undermined if sidecar queries queue up excessively.