Queries to last cache with large `IN` list predicates seem slow

The performance team has observed that when querying the last cache with `IN` clauses with ~100 elements leads to response times on the order of ~30ms.

For example,
```sql
SELECT * FROM last_cache('table_name', 'cache_name') where key_columns IN ('random value 1', ... 'random value 100');
```

This issue is for tracking whether or not this can be improved.

Start by reproducing the SQL example against last_cache with an IN list of about 100 elements and measure the roughly 30 ms response time. Trace the last_cache query path and compare this case with smaller IN lists; done means demonstrating a measurable improvement or documenting why the behavior cannot be improved.

Written by the indexing model from the issue text.