fix: Fix cleanup in test helpers, prefer defer in tests (#3113)

* fix: Change uses of t.Cleanup -> defer in test bodies

Mixing t.Cleanup and defer can lead to unexpected order of execution.

* fix: Ensure t.Cleanup is not aborted by require

* chore: Add helper annotations

cli/server_test.go

@@ -249,7 +249,7 @@ func TestServer(t *testing.T) {
 			snapshot <- ss
 		})
 		server := httptest.NewServer(r)
-		t.Cleanup(server.Close)
+		defer server.Close()
 
 		root, _ := clitest.New(t, "server", "--in-memory", "--address", ":0", "--telemetry", "--telemetry-url", server.URL)
 		errC := make(chan error)