[SPARK-51096][SQL][TESTS] Splitting TransformWithStateSuite into UnsafeRow and Avro encoding suites

### What changes were proposed in this pull request?

Splitting the TransformWithStateSuite into TransformWithStateUnsafeRowEncodingSuite and TransformWithStateAvroEncodingSuite, in order to remove it from the slow test category

### Why are the changes needed?

To remove TransformWithState-related suites from the Slow test category

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

Just moving tests around, no need to test

### Was this patch authored or co-authored using generative AI tooling?

No

Closes #49815 from ericm-db/split-tws-suite.

Authored-by: Eric Marnadi <[email protected]>
Signed-off-by: Jungtaek Lim <[email protected]>
(cherry picked from commit 9dbbb5b)
Signed-off-by: Jungtaek Lim <[email protected]>

Author: ericm-db