Filtered navigation scans one pokemon at a time

[ayushb]

GetNextFiltered and GetPrevFiltered walk the ids one by one, fetching every pokemon until one matches the filter.

With a sparse type filter, filling an 11 item list means a lot of sequential requests. With a filter combination that matches nothing, it fetches all 1025 in both directions before giving up.

That works against the "ingen unødvendige kall til REST API'et" criterion.

PokeAPI has /api/v2/type/{name} which returns every pokemon of a type in one request. Using that to get the candidate ids first, then fetching only those, would replace the scan.

Came out of the review on #26.

[ayushb]

Done in #33, merged to main (5b02d49). Filtered next/prev now looks up the members of a type in one request instead of walking every id.