internal/pkg: pass impure job count

This is cleaner than checking cpu count during cure, it is impossible to avoid impurity in both situations but this is configurable.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa_test.go

@@ -60,7 +60,7 @@ func getCache(t *testing.T) *pkg.Cache {
 			msg := message.New(log.New(os.Stderr, "rosa: ", 0))
 			msg.SwapVerbose(true)
 
-			if buildTestCache, err = pkg.Open(ctx, msg, 0, 0, a); err != nil {
+			if buildTestCache, err = pkg.Open(ctx, msg, 0, 0, 0, a); err != nil {
 				t.Fatal(err)
 			}
 		}