rp_query.fetch_test_item should support filters as parameters.

Currently `rp_query.fetch_test_item` builds filters based only on global options, and it is not possible to reuse this call, with more specific filtering.

- [ ] add a filter parameter to the function that would be then applied
- [ ] refactor the default behavior of building filters from options to make it more reusable
- [ ] update related tests

Start by locating `rp_query.fetch_test_item` and read the related tests to understand how global options currently build filters. Add support for a filter parameter while preserving the default behavior, then update the related tests to cover both custom filters and option-derived filters.

Written by the indexing model from the issue text.