[SPARK-50970][PYTHON][SS] Unify naming convention for stateful processor APIs

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

Unify naming convention for stateful processor APIs.

### Why are the changes needed?

Following best practice, make TransformWithStateInPandas naming convention consistent across APIs.

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

Yes.

### How was this patch tested?

Existing unit test.

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

No.

Closes #49636 from bogao007/python-tws-syntax.

Authored-by: bogao007 <[email protected]>
Signed-off-by: Jungtaek Lim <[email protected]>

Author: bogao007

python/pyspark/sql/pandas/group_ops.py

@@ -566,8 +566,8 @@ def handle_expired_timers(
                     statefulProcessorApiClient.set_implicit_key(key_obj)
                     for pd in statefulProcessor.handleExpiredTimer(
                         key=key_obj,
-                        timer_values=TimerValues(batch_timestamp, watermark_timestamp),
-                        expired_timer_info=ExpiredTimerInfo(expiry_timestamp),
+                        timerValues=TimerValues(batch_timestamp, watermark_timestamp),
+                        expiredTimerInfo=ExpiredTimerInfo(expiry_timestamp),
                     ):
                         yield pd
                     statefulProcessorApiClient.delete_timer(expiry_timestamp)