PREWHERE (and similar native constructs) don't work with unit tests

### Describe the bug

PREWHERE (and similar native constructs) don't work with unit tests. We leverage PREWHERE in certain performance-critical models where we are certain that we can run FINAL after PREWHERE.

### Steps to reproduce (with pseudo code)

```
#_my_fancy_model_
select *
from {{ source("raw", "my_fancy_source") }}
prewhere id = 5
```

1. Implement a model with a PREWHERE filtering on an arbitrary source table's column.
2. Run a unit test for the model
3. Error:

Received ClickHouse exception, code: 182, server response: Code: 182. DB::Exception: Invalid column __table3.id in PREWHERE. Expected column source to be table or table function. Actual __dbt__cte__my_fancy_model ...

### Expected behaviour

Should be able to perform PREWHERE filtering on the sources.

I believe the issue stems from the fact unit test sources (sources, not the model itself, but sources!) in `given` are inlined as CTEs instead of seeds or temporary tables. Clickhouse disallows to prewhere filter on CTEs.

Any ideas how to approach this? Don't think dbt will release a fix anytime soon, since it's a Clickhouse-specific issue... We're thinking of overriding this (somehow) locally, but maybe we could implement something within the level of this adapter.

Start by reproducing the unit test with a source CTE and PREWHERE, then inspect how sources supplied in `given` are inlined during unit-test compilation. Compare that generated query with ClickHouse's PREWHERE restriction on CTEs; done means the unit test can apply PREWHERE to the source without the reported exception.

Written by the indexing model from the issue text.