Fix x360 packet len and keychron

[thor27]

Fix: #374

Add support for Keychron keyboards running in Xbox gamepad emulation mode.

Besides adding the id support, to get proper button working, we also need to change the packet size to 32bits.

I think 64bits package, as per git history, is only for Xbox One controller, so this fix should improve compatibility with previous and older non standard controller:

Modern xpad hardcodes XPAD_PKT_LEN = 64 for all incoming interrupt URBs
to accommodate Xbox One controllers. However, Xbox 360 and classic Xbox
devices communicate using 32-byte frames (wMaxPacketSize = 32).

On USB endpoints that emit 32-byte reports without Zero-Length Packets
(such as high-polling composite devices), requesting 64 bytes causes
the host controller to defer URB completion until two 32-byte packets
accumulate. This leads to paired/lagged inputs and unreleased button
states while stationary.

Separate the buffer allocation size (kept at 64 bytes for DMA safety)
from the transfer buffer length, setting in_len to 32 bytes for
non-Xbox-One devices.

I used Gemini to help me identify the problem and write commit messages.
Testing and coding was done by me.