Add Long-Press (Hold) Support and UI Improvements to Speedtest Plugin

[parkour86]

Overview

This pull request introduces enhancements to the Speedtest plugin, improving its user interaction and UI feedback.

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Key Changes

1. Long-Press (Hold) Support

• Added an event_callback method to the Speedtest action class, mirroring the event handling style of other plugins (such as the Counter plugin).
• Implemented an on_key_hold method that is triggered on long-press (HOLD_START event).
• When the button is held, the plugin now:
  • Clears the top and center labels and resets the bottom label to "Start".
  • Restores the default speedtest image (speed.png) to the button, ensuring the UI resets after a test or error.

2. UI Consistency

• Ensured that after a speed test or error, holding the button will always restore the original image and clear any test results or error messages from the labels.

3. Non-breaking Changes

• The original short-press (on_key_down) behavior is preserved and now routed through the new event handling system for consistency with other plugins.