Improve multi-gpu handling at the limit

Still not complete, needs some refinement to our prediction to understand the
discrete GPUs available space so we can see how many layers fit in each one
since we can't split one layer across multiple GPUs we can't treat free space
as one logical block

integration/context_test.go

@@ -11,7 +11,7 @@ import (
 )
 
 func TestContextExhaustion(t *testing.T) {
-	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute) // TODO maybe shorter?
+	ctx, cancel := context.WithTimeout(context.Background(), 4*time.Minute) // Longer needed for small footprint GPUs
 	defer cancel()
 	// Set up the test data
 	req := api.GenerateRequest{