[PECOBLR-3984] Add jitter to chunk download retries

[prathamesh-db]

Description

Adds equal jitter (750–1,500 ms) to the existing chunk-download retry delay in both batch and streaming paths. This reduces synchronized retry bursts while preserving five attempts and the existing six-second maximum total retry wait.

Jira: https://databricks.atlassian.net/browse/PECOBLR-3984

Testing

• Added deterministic coverage for both jitter boundaries.
• Updated batch and streaming tests to verify the selected nonzero delays reach the sleep path.
• Spotless passes; the focused Maven suite passes all 10 tests.

Telemetry Errors

• Not applicable — this PR does not add or change a telemetry-visible error.
• Applicable — the error uses DatabricksDriverErrorCode where appropriate, and any new code is uniquely numbered and tested.
• Applicable — its driver/server/user classification is linked, or maintainer help is requested because the author cannot access the classification.

Additional Notes to the Reviewer

The retry count and existing CHUNK_DOWNLOAD_ERROR telemetry code are unchanged. This mitigation reduces correlated retries; it does not claim to eliminate every chunk-download failure.

This draft PR was generated by the PECO Agent Workflow and then narrowed to the telemetry-backed mitigation above.