Remove redundant getSnapshotAt calls per commit

[brishi19791]

This PR removes redundant DeltaLog.getSnapshotAt(version) calls in the Delta source conversion path that were happening for every commit. getSnapshotAt can internally trigger an expensive Spark job and associated network I/O (e.g., listing/reading Delta log metadata from remote storage) to resolve the snapshot for a given version. We now fetch the snapshot once per commit/version and reuse it to construct the InternalTable (via a DeltaTableExtractor.table(Snapshot, tableName) overload), instead of re-resolving the same snapshot multiple times.

Impact

• Avoids redundant snapshot resolution work per commit/version (and the Spark job + network calls it may trigger).
• Reduces end-to-end conversion latency, especially for large commit backlogs.
• No intended functional behavior change; performance optimization only.

[kevinjqliu]

We now fetch the snapshot once per commit/version and reuse it to construct the InternalTable (via a DeltaTableExtractor.table(Snapshot, tableName) overload), instead of re-resolving the same snapshot multiple times.

Thats awesome, thanks for adding the perf improvement. It might be a good idea to add a test (either here or a follow up PR) to verify that the entire conversion process should only read the DeltaLog once.