feat: HDMI refresh boost (Steam Machine, pinned kernel)

The pinned 7.1.6 kernel doesn't read the extra EDID block (HDMI Forum
EEODB) where monitors list their fast modes, and does no HDMI 2.1, so HDMI
displays often stay at 60 Hz. The new menu item reads the display's EDID
over DDC, calculates the highest rate that fits HDMI 2.0 at the desktop
resolution (rounded down to ten, plus the hundred below as a safe option),
tests each step live with a confirmation, and makes the confirmed ones
permanent through drm.edid_firmware (Limine, sdboot-manage or GRUB).

README.md

@@ -50,6 +50,12 @@ What Steamify can do on a Valve Steam Machine:
     [release](https://github.com/theupriser/steamify-cachyos/releases/tag/kernel-7.1.6-1),
     checked against CachyOS's signature
     ([details](TECHNICAL.md#kernel-pin-steam-machine)).
+- **HDMI refresh boost** - only with the pinned kernel, never ticked by
+  default: gets the highest refresh rate your HDMI display runs at the
+  desktop resolution (e.g. 110 Hz instead of 60 on a 3440x1440 monitor).
+  Each step is shown and you confirm it; no answer within 15 s switches
+  back. For more (e.g. 175 Hz), use DisplayPort
+  ([details](TECHNICAL.md#hdmi-refresh-boost-steam-machine)).
 - **Update BIOS** - installs Valve's newest Steam Machine BIOS. Never ticked
   by default, at your own risk, and only after two warnings
   ([details](TECHNICAL.md#bios-updates-steam-machine)).