Allow_partials option is updating last completed interval too

[mpcarter]

When using the allow_partials true option in an INCREMENTAL_BY_TIME_RANGE model, SQLMesh is refreshing the most recent completed interval along with the current incomplete (partial) interval.

I have not fully vetted if this happens generally, but I observed this happen with a scenario similar to this model:

MODEL (
    name dw.monthly_stats ,
    kind INCREMENTAL_BY_TIME_RANGE (
        time_column as_of_month ,
        batch_size 1 
    ), 
    cron '@daily' ,
    interval_unit month ,
    allow_partials true 
);

The intent is to have the current month interval refresh daily.

As of writing this, 2/18/2025 using SQLMesh v0.156.0, here is the sequence of events I observed:

1. Initially load the model- For each month before 1/1/2025, SQLMesh runs a query using the first and last date of the month, as expected e.g.
   1/1/2024 - 1/31/2024, ... , 11/1/2024 - 11/30/2024, 12/1/2024 - 12/31/2024.
2. During initial load still- For Jan and Feb 2025, the last complete interval and current interval, SQLMesh runs one query using 1/1/2025 - 2/xx/2025 (xx being dependent on what day in Feb initial load is done).
3. Running sqlmesh plan --restate-model -s 2025-01-01 -e 2025-02-xx results in same effect. One query runs to populate both intervals.
4. Running sqlmesh plan --restate-model -s 2025-01-01 -e 2025-01-31 results in correct effect of populating just the Jan 2025 interval.
5. Running sqlmesh run (the day after initial load) results in SQLMesh again running one query using 1/1/2025 - 2/xx+1/2025 to populate both intervals despite the fact that the Jan 2025 interval is already loaded

What I would expect to occur is that the initial load would populate Jan 2025 separately from Feb 2025 (the current partial interval) using 1/1/2025 - 1/31/2025 for Jan, and 2/1/2025 - 2/xx/2025 for Feb.
For subsequent sqlmesh run I would expect that only Feb 2025 would be refreshed using 2/1/2025 - 2/xx/2025.

Actually, on that last point, it would be preferable if the end date was always based on the boundaries of the intervals. E.g. in this case where interval_unit month, the current partial interval Feb 2025 would always use 2/1/2025 - 2/28/2025 each day it is refreshed.