Fix lint errors: handle errors, use fmt.Fprintf, apply De Morgan's law, use switch statements

Amp-Thread-ID: https://ampcode.com/threads/T-afcf56b0-a8bc-4310-bb59-1b63e1d70c89
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/daemon_test.go

@@ -249,7 +249,7 @@ func TestDaemonLogFileCreation(t *testing.T) {
 
 	timestamp := time.Now().Format("2006-01-02 15:04:05")
 	msg := "Test log message"
-	_, err = logF.WriteString(fmt.Sprintf("[%s] %s\n", timestamp, msg))
+	_, err = fmt.Fprintf(logF, "[%s] %s\n", timestamp, msg)
 	if err != nil {
 		t.Fatalf("Failed to write to log file: %v", err)
 	}