Remove `list_as_series=True` from `search_sorted`

[coastalwhite]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl
df = pl.DataFrame({ 'a': [1, 2, 3, 4, 5, 6, 7] })

df.select(
    search_sorted = pl.col.a.search_sorted([1, 2]), # returns [0, 1]
    index_of = pl.col.a.index_of([1, 2]) # throws error
)

Log output

Issue description

I think it is strange that search_sorted and index_of show different behavior.

Expected behavior

In my mind, either one should be like the other.

Installed versions

Replace this line with the output of pl.show_versions(). Leave the backticks in place.

[mcrumiller]

Both the index_of and the search_sorted documentation expects that element is a scalar value. I think that this should go into the "make sure it's a scalar" bucket. Calling index_of([1, 2]) should throw an error "expected scalar value, got list [1, 2]" or something.

On another note though, I don't see why either of these shouldn't expect lists. AFAIK we don't have the equivalent of np.argwhere which would be nice.

[coastalwhite]

I think this is because of the list_as_series=True on search_sorted.

[coastalwhite]

Yeah, after some further investigation the behavior from search_sorted is not necessarily wrong. It should should not have the flag list_as_series=True. Sadly, we cannot break this until 2.0.