Add wireless battery reporting to Keychron raw HID

[shayangohar]

Description

This adds an opt-in wireless raw HID path to Keychron's common firmware and exposes the cached battery percentage to host utilities.

The change:

• Adds KC_GET_BATTERY_LEVEL (0xA4).
• Returns the battery percentage in response byte 1.
• Routes wireless EVT_RAW_HID events through the normal raw_hid_receive() handler.
• Corrects the misspelled WILRESS_RAW_ENABLE define to WIRELESS_RAW_ENABLE.
• Updates documentation accordingly to record the command and opt-in build define
• Keeps wireless transport routing disabled unless a keyboard explicitly defines WIRELESS_RAW_ENABLE.

This allows a Keychron 2.4 GHz receiver to report keyboard battery status without using Bluetooth. It does not modify receiver firmware, battery calculation, key behavior, or Bluetooth behavior.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Verification

• git diff --check passes.
• The change is based on Keychron's 2025q3 branch.
• The combined common-core and K8 HE opt-in firmware was built successfully.
• The resulting firmware was tested on a Keychron K8 HE using the Keychron 2.4 GHz receiver.
• A tray utility successfully retrieved a valid battery percentage over 2.4 GHz.
• Keyboard worked fine with no issues over wired connection, 2.4 GHz, and Bluetooth.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).