treewide: parallel tests

Most tests already had no global state, however parallel was never enabled. This change enables it for all applicable tests.

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

internal/app/app_test.go

@@ -28,6 +28,7 @@ import (
 )
 
 func TestApp(t *testing.T) {
+	t.Parallel()
 	msg := message.NewMsg(nil)
 	msg.SwapVerbose(testing.Verbose())
 
@@ -445,6 +446,7 @@ func TestApp(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
 			gr, gw := io.Pipe()
 
 			var gotSys *system.I