[Spark] Expand UC Delta ALTER TABLE integration tests

[TimothyW553]

Which Delta project/connector is this regarding?

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

Description

Follow-up to the testing breadth requested in #6840.

Expands the sparkuctest coverage for UC Delta ALTER TABLE behavior after #6840. This splits the broad ALTER TABLE smoke test into focused integration cases and adds coverage for:

• custom table property SET/UNSET
• delta.autoOptimize.* SET/UNSET behavior
• protocol-derived property no-op commits for delta.feature.catalogManaged and delta.minReaderVersion
• ADD COLUMNS with multiple data types
• column comments and table comments
• feature-backed table properties such as CDF
• cluster key updates with SHOW TBLPROPERTIES validation

How was this patch tested?

./build/sbt sparkUnityCatalog/javafmtAll
./build/sbt "sparkUnityCatalog/testOnly io.sparkuctest.UCDeltaTableAlterTest"

The focused suite passed with 21 tests.

Does this PR introduce any user-facing changes?

No. Test-only change.