Fix error when filter value not found in items set

Enhancement:

Flexible Filtering: The library now gracefully handles non-existing filter values thanks to PR #130 .
Scenario: If you have default filter categories like "comedy", "drama", or "thriller", but the data only contains "comedy" and "drama", the system won't crash. Instead, it adapts to the available items.
Technical Detail: Introduced a fallback to an empty FastBitset to ensure stability.