feat: Implement fix for sunlight fading issue (#603)

## Summary

* **What is the goal of this PR?**

The goal of this PR is to deliver a fix for or at least mitigate the
impact of the issue described in #561

* **What changes are included?**

This PR includes a new option "Sunlight Fading Fix" under "Settings ->
Display".

When set to ON, we will disable the displays analog supply voltage after
every update and turn it back on before the next update.

## Additional Context

* Until now, I was only able to do limited testing because of limited
sunlight at my location, but the fix seems to be working. I'll also
attach a pre-built binary based on 0.16.0 (current master) with the fix
applied to the linked ticket, as building this fix is a bit annoying
because the submodule open-x4-sdk also needs an update.
* [PR in
open-x4-sdk](https://github.com/open-x4-epaper/community-sdk/pull/15)
needs to be merged first, we also need to add another commit to this
here PR, updating this dependency.
* I decided to hide this behind a default-OFF option. While I'm not
really concerned that this fix might potentially damage the display,
someone more knowledgeable on E-Ink technology could maybe have a look
at this.
* There's a binary attached in the linked issue, if someone has the
required sunlight to test this in-depth.

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

USER_GUIDE.md

@@ -150,6 +150,9 @@ The Settings screen allows you to configure the device's behavior. There are a f
 - **Reader Paragraph Alignment**: Set the alignment of paragraphs; options are "Justified" (default), "Left", "Center", or "Right".
 - **Time to Sleep**: Set the duration of inactivity before the device automatically goes to sleep.
 - **Refresh Frequency**: Set how often the screen does a full refresh while reading to reduce ghosting.
+- **Sunlight Fading Fix**: Configure whether to enable a software-fix for the issue where white X4 models may fade when used in direct sunlight
+  - "OFF" (default) - Disable the fix
+  - "ON" - Enable the fix
 - **OPDS Browser**: Configure OPDS server settings for browsing and downloading books. Set the server URL (for Calibre Content Server, add `/opds` to the end), and optionally configure username and password for servers requiring authentication. Note: Only HTTP Basic authentication is supported. If using Calibre Content Server with authentication enabled, you must set it to use Basic authentication instead of the default Digest authentication.
 - **Check for updates**: Check for firmware updates over WiFi.