Feature: Redesign firmware processing to use URL-based fetch and local cache

[fxstein]

Redesign the firmware processing logic in GoProX to remove all firmware zip files from the repository. Instead, use the URLs provided in the existing shortcut files to fetch the required firmware file directly from the internet when needed, storing it in a local cache directory.

When processing firmware for a camera, the script should:

• Check if the required firmware zip is already present in the local cache.
• If not, download it from the URL in the shortcut file and store it in the cache.
• If already cached, use the local copy for subsequent firmware updates (e.g., for other cameras).
• Copy the firmware from the cache to the SD card as needed.
• Add an extension/option to GoProX to clear the local firmware cache.