[SPARK-50378][SS] Add custom metric for tracking spent for proc initial state in transformWithState

[anishshri-db]

What changes were proposed in this pull request?

Add custom metric for tracking spent for proc initial state in transformWithState

Why are the changes needed?

Adds tracking for time spent in populating initial state

Does this PR introduce any user-facing change?

No

How was this patch tested?

Added unit tests

[info] Run completed in 2 minutes, 38 seconds.
[info] Total number of tests run: 22
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 22, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.

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

No

[anishshri-db]

cc - @HeartSaVioR - PTAL, thx !

[HeartSaVioR]

+1
Will we have a separate PR to address this in PySpark impl? I guess the execution model may not be exactly the same, but if feasible, better to be consistent.

[HeartSaVioR]

I'll leave it to you; I won't block this PR just to ensure consistency.

Thanks! Merging to master.