runner: default to greedy sampler for performance (#9407)

As are adding support for weighted sampling we have seen some performance
regressions, bypassing the sampler logic for now and defaulting to greedy
until we can benchmark the new sampler logic.

runner/ollamarunner/runner.go

@@ -575,23 +575,11 @@ func (s *Server) completion(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	sampler, err := sample.NewSampler(
-		req.Temperature,
-		req.TopK,
-		req.TopP,
-		req.MinP,
-		req.Seed,
-	)
-	if err != nil {
-		http.Error(w, fmt.Sprintf("Failed to create sampler: %v", err), http.StatusInternalServerError)
-		return
-	}
-
 	seq, err := s.NewSequence(req.Prompt, req.Images, NewSequenceParams{
 		numPredict: req.NumPredict,
 		stop:       req.Stop,
 		numKeep:    int32(req.NumKeep),
-		sampler:    sampler,
+		sampler:    sample.Greedy(), // TODO: add support for different samplers when performance is optimized
 		embedding:  false,
 	})
 	if err != nil {