Get opening vs closing line values (OLV/CLV) for a fixture.
Lookup mode: required fixtureId + optional bookmakers OR optional oddsIds.
Your API key (query-based auth for v5).
Single fixture ID (e.g. id1400003160574219).
Comma/space-separated bookmaker slugs (default: all).
Optional: comma/space-separated oddsIds to restrict the response.
Returns FixtureClvResponse (fixture meta + OLV/CLV pairs)