Integrate latest driver update into older Zephyr version manually

[BionicCode]

Hi guys,
I'm designing hardware and I desperately need to support the FUSB307 and PF1550 devices.

I was happy to find out that the required FUSB307 driver has just been added to the main branch two weeks ago.
However, this means, it won't be available until the release of Zephyr 4.2 or later.

The driver for the PF1550 has been released with Zephyr 4.1

The problem, I'm using ZMK, which builds on top of Zephyr. ZMK is using Zephyr 3.5 (the upgrade to v4.1 is on the agenda, but we can't expect it to be released earlier than two month, which is a pretty optimistic estimate).

I was now wondering if I could fork the repo and add the drivers manually to bridge the time until the official release.
This would allow me to continue wit the development, and more importantly, stick to the current hardware choices.

1. First of all, is it possible to add the individual drivers for the PF1550 (part of Zephyr 4.1) and FUSB307 (unreleased, main branch) to Zephyr 3.5 or are there any dependencies that the v3.5 can't provide (and are difficult to migrate)?

2. And if so, could somebody please give me a summary of the steps that are required?
   Is it safe to follow and replicate the change history of the merge request? Or is it missing something crucial?

I'm aware, I have to add the sources, modify the cmakelist and kconfig.

3. If the driver for the FUSB307 was added to the main branch, can we assume it has been tested and was therefore eligible to be merged into the main branch? Or is the source code unsafe/unreliable? Following common practice I would expect sources in the main branch to be ready for a release draft, I just want make sure.

Thanks for your help!