[CELEBORN-2415] Add Celeborn Spark UI extension

[yew1eb]

What changes were proposed in this pull request?

Add a new module celeborn-client-spark-3-ui — a Spark UI extension that renders a "Celeborn" tab in both the live Spark UI and the History Server (enabled via spark.plugins=org.apache.spark.shuffle.celeborn.CelebornPlugin, supports Spark 3.x and 4.x).

This is an initial version that lays the foundation; it intentionally starts minimal. The page shows:

1. Summary — shuffle write/read bytes, time, speed, and shuffle-vs-task duration ratio, aggregated from Spark's built-in TaskMetrics
2. Celeborn Properties — a collapsible table of spark.celeborn.* configs

The skeleton is: CelebornPlugin (live UI) / CelebornHistoryServerPlugin (SHS, via AppHistoryServerPlugin SPI) → listener aggregates into Spark KVStore → CelebornStatusStore → CelebornUITab renders; a javax/jakarta servlet bridge covers Spark 3.x and 4.x. This plugin/store/render pipeline is designed so that fine-grained Celeborn client metrics can be added as collapsible sections in follow-up PRs:

• Shuffle Write Times — serialize / copy / queue wait / compress / queue stall / inflight wait / drain wait / max push RTT / slow push
• Shuffle Read Times — chunk wait / decompress / retry wait / max chunk RTT / slow chunk
• Shuffle Write Servers — per-worker push bytes, push count, RTT, soft/hard splits, congested counts, last failure reason
• Shuffle Read Servers — per-worker chunk count, read bytes, total/max RTT
• Shuffle Assignments — partition-to-worker slot assignments

Why are the changes needed?

Spark UI already shows stage/task-level shuffle metrics, but nothing Celeborn-specific: which workers served the data, push/chunk latencies, congestion and split events are invisible there, while Celeborn's own metrics sit in cluster-level Grafana dashboards that cannot be attributed back to a specific application. This tab closes that gap by putting per-application Celeborn shuffle information inside the Spark UI and History Server, alongside the job's stages and tasks.

Does this PR introduce any user-facing change?

Yes.
Setting spark.plugins=org.apache.spark.shuffle.celeborn.CelebornPlugin (with the extension jar on the classpath) adds a "Celeborn" tab to the Spark UI and History Server. Disabled by default; no effect otherwise.

Does this PR resolve a correctness bug?

No.

How was this patch tested?

Manual end-to-end verification:

[yew1eb]

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