[CELEBORN-2226][CIP-14] Support RetryFetchChunk functionality for Cel…

[afterincomparableyum]

Implement chunk-fetch retry logic in CelebornInputStream::getNextChunk(), matching the Java CelebornInputStream behavior. When a chunk fetch fails, the retry loop excludes the failed worker, switches to the peer replica (if available), and sleeps between retry rounds before creating a new reader.

Added getLocation() to PartitionReader interface and WorkerPartitionReader

Replaced the stub getNextChunk() with full retry logic: excluded worker checks, peer switching, configurable retry count, sleep between retries

Updated moveToNextChunk() and moveToNextReader() to handle nullable returns from getNextChunk()

Added unit test for WorkerPartitionReader::getLocation()

Added unit tests for getNextChunk() retry logic

CI and build passes

[afterincomparableyum]

I will rebase off of main and then open this PR once #3583 gets merged.

[jaystarshot]

@afterincomparableyum thanks for these changes, do you have a list of unsupported functionality in the cpp client by any chance?

[afterincomparableyum]

@jaystarshot these are the ones I am working on.

I have local changes for most of them made already, just opening PRs sequentially based on dependency on previous PRs.
https://issues.apache.org/jira/browse/CELEBORN-2199

[afterincomparableyum]

Ping @HolyLow @SteNicholas @RexXiong for review.

[Copilot]

Pull request overview

Adds chunk-fetch retry behavior to the C++ Celeborn client input stream (mirroring Java behavior), including worker exclusion checks and peer-replica switching, and exposes a reader’s PartitionLocation to support that logic.

Changes:

• Added getLocation() to the PartitionReader interface and implemented it in WorkerPartitionReader.
• Replaced the CelebornInputStream::getNextChunk() stub with retry/exclusion/peer-switching logic and updated reader/chunk advancement to handle nullptr chunks.
• Added a unit test validating WorkerPartitionReader::getLocation().

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
cpp/celeborn/client/tests/WorkerPartitionReaderTest.cpp	Adds a unit test for WorkerPartitionReader::getLocation().
cpp/celeborn/client/reader/WorkerPartitionReader.h	Extends PartitionReader with getLocation() and declares override in WorkerPartitionReader.
cpp/celeborn/client/reader/WorkerPartitionReader.cpp	Implements WorkerPartitionReader::getLocation().
cpp/celeborn/client/reader/CelebornInputStream.cpp	Implements chunk-fetch retry logic and updates chunk/reader progression to tolerate nullptr from getNextChunk().

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[SteNicholas]

@afterincomparableyum, thanks for contribution. I left minor comment for the changes. In addition, please take a look at the review comments of Copilot.

[afterincomparableyum]

Comments resolved @SteNicholas , and CI should pass as well.