UDF checkpoints followup

[ilongin]

List of follow up issues after UDF checkpoints is merged.

• UDF Checkpoints cleanup #1453
• Implement UDF checkpoints for aggregator #1469
• Flush insert buffer based on time #1519
• Use run_group_id + hash for UDF input table name #1521
• Add ability in UI to reset UDF checkpoint
• Fix limitation where inputs yielding nothing are not tracked in processed table in generator.
• https://github.com/datachain-ai/studio/issues/12370