refactor: Reorganise file structure

Signed-off-by: quexeky <git@quexeky.dev>

desktop/src-tauri/src/error/download_manager_error.rs

@@ -0,0 +1,27 @@
+use std::{fmt::Display, io, sync::mpsc::SendError};
+
+use serde_with::SerializeDisplay;
+
+#[derive(SerializeDisplay)]
+pub enum DownloadManagerError<T> {
+    IOError(io::Error),
+    SignalError(SendError<T>),
+}
+impl<T> Display for DownloadManagerError<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            DownloadManagerError::IOError(error) => write!(f, "{}", error),
+            DownloadManagerError::SignalError(send_error) => write!(f, "{}", send_error),
+        }
+    }
+}
+impl<T> From<SendError<T>> for DownloadManagerError<T> {
+    fn from(value: SendError<T>) -> Self {
+        DownloadManagerError::SignalError(value)
+    }
+}
+impl<T> From<io::Error> for DownloadManagerError<T> {
+    fn from(value: io::Error) -> Self {
+        DownloadManagerError::IOError(value)
+    }
+}