feat: Resumable Download Helper and Manifest Preservation

- Route downloads through local cache directory
- Automatically resume interrupted downloads from the byte offset
- `setup_uninstaller_context` checks if a fail had happened. If yes then
  CLI preserves existing manifest instead of wiping it.
- Interruption Signal Traps and Prompts

installers/install_rust.sh

@@ -76,7 +76,7 @@ install_rust() {
     local dest="$TMP_DIR/rustup-init"
 
     log_info "Downloading rustup-init..."
-    curl -fsSL "$url" -o "$dest"
+    download_file "$url" "$dest"
 
     chmod +x "$dest"