SC-211135: Implement analyzer rule for V2 streaming reads

[vitaliili-db]

This implements Option A from the design doc: using an analyzer rule to replace V1 (DeltaTableV2) with V2 (SparkTable) for streaming reads only.

Key changes:

• Add UseKernelForStreamingRule analyzer rule in spark-unified module
• Rule pattern matches on StreamingRelationV2 to isolate streaming reads
• Add DELTA_KERNEL_STREAMING_ENABLED config flag (default: false)
• Register rule in DeltaSparkSessionExtension

Behavior:

• Streaming reads (readStream) → V2 (Kernel-based, MicroBatchStream)
• Streaming writes (writeStream) → V1 (DeltaLog-based)
• Batch reads/writes → V1 (DeltaLog-based)
• MERGE/UPDATE/DELETE → V1 (DeltaLog-based)

This approach:

• Requires zero user code changes
• Works with existing V1 and V2 implementations unchanged
• Enables gradual rollout via configuration flag
• Provides graceful fallback on errors

Which Delta project/connector is this regarding?

• [ ] Spark
• [ ] Standalone
• [ ] Flink
• [ ] Kernel
• [ ] Other (fill in here)

Description

How was this patch tested?

Does this PR introduce any user-facing changes?