Request and model concurrency

This change adds support for multiple concurrent requests, as well as
loading multiple models by spawning multiple runners. The default
settings are currently set at 1 concurrent request per model and only 1
loaded model at a time, but these can be adjusted by setting
OLLAMA_NUM_PARALLEL and OLLAMA_MAX_LOADED_MODELS.

integration/basic_test.go

@@ -4,7 +4,6 @@ package integration
 
 import (
 	"context"
-	"net/http"
 	"testing"
 	"time"
 
@@ -24,5 +23,5 @@ func TestOrcaMiniBlueSky(t *testing.T) {
 			"seed":        123,
 		},
 	}
-	GenerateTestHelper(ctx, t, &http.Client{}, req, []string{"rayleigh", "scattering"})
+	GenerateTestHelper(ctx, t, req, []string{"rayleigh", "scattering"})
 }