Fix!: Handle lookback correctly on incremental models with an end date defined

[erindru]

Slack context: https://tobiko-data.slack.com/archives/C044BRE5W4S/p1721917406454879

This PR allows lookback to return the correct missing intervals if the execution date is beyond the model's end date. Prior this, sqlmesh run would always show a phantom interval for these models even if the current date was well beyond the model end date + lookback period.

Assuming an incremental model with an end date of 2023-01-05, @daily intervals and a lookback of 2 days:

• The user does not want data from the source system beyond 2023-01-05 so they don't want new intervals after 2023-01-05
• However, they do want already run intervals to re-run after 2023-01-05 if they are within the lookback period
• So the following intervals would run on the following days:
  • 2023-01-05 -> 2023-01-05, 2023-01-04, 2023-01-03
  • 2023-01-06 -> 2023-01-04, 2023-01-05
  • 2023-01-07 -> 2023-01-05
  • 2023-01-08 -> (none, we are done)