Validate-or-build function

[benrutter]

For some file based workflows, something like this would be nice:

import polars as pl
import wimsey

def some_function() -> pl.DataFrame:
    return (
        get_some_polars_table()
        .with_columns(a=pl.col("b") - pl.col("c"))
        .pipe(wimsey.validate_or_create_tests, location="some/test/location.yaml")
    )

i.e. if a test doesn't exist, will use sampling to generate some "starter tests" and save them. But if they do exist, will then test according to them.