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_starship.sh

@@ -59,7 +59,7 @@ install_starship() {
 
     log_info "Downloading Starship from ${download_url}..."
     local archive="$TMP_DIR/starship.tar.gz"
-        curl -fsSL "$download_url" -o "$archive"
+    download_file "$download_url" "$archive"
 
     # Extract the binary
     log_info "Extracting Starship binary..."