cubered: add CubeRed platform and secondary MCU update flow

[HTRamsey]

Summary

This PR adds CubeRed support and an explicit secondary-MCU update flow in two commits:

1. cubered: add board support and secondary packaging pipeline

• Adds boards/cubepilot/cubered/* board bringup/config.
• Adds CubeRed bootloader binary to bootloaders_update.
• Adds Tools/build_cubered_secondary_from_ardupilot.py for optional secondary artifact generation.
• Adds secondary package generation wiring in NuttX CMake.

2. bootloader/uploader: add secondary MCU update flow

• Adds bootloader SERIAL_FORWARD support and secondary UART path for host<->secondary passthrough.
• Adds uploader update modes (primary|secondary|both|auto) and dual-image upload orchestration.
• Adds runtime secondary update hooks (SYS_SEC_UPDATE, rc.board_secondary_upgrade, rcS integration).
• Adds uploader unit tests and Python CI coverage.

Notes

• Secondary flow is explicit and can be disabled by default via CMake switch.
• Default upload path remains primary-only unless secondary mode/targets are selected.

Test

• python3 -m unittest discover -s test -p 'test_px4_uploader.py'

[dirksavage88]

@julianoes any idea on how to get the firmware on the io processor for this cube?

[dirksavage88]

Are these changes relevant? What is driving this change for the imxrt processors?

[HTRamsey]

can be removed. Was just consistency with what I changed in the other bootloader folders

[dirksavage88]

We may want to split this functionality into a separate PR:

bootloader/uploader: add secondary MCU update flow
Adds bootloader SERIAL_FORWARD support and secondary UART path for host<->secondary passthrough.
Adds uploader update modes (primary|secondary|both|auto) and dual-image upload orchestration.
Adds runtime secondary update hooks (SYS_SEC_UPDATE, rc.board_secondary_upgrade, rcS integration).
Adds uploader unit tests and Python CI coverage.

[julianoes]

@HTRamsey that's awkward: https://github.com/julianoes/PX4-Autopilot/tree/pr-cubered

I guess I'll do some diffing to check if you (or I) missed anything.

[HTRamsey]

Oh damn my bad I really should have checked first. Please go ahead and do your thing, you'll do a lot better than me. I just had a cube red temporarily and figured I'd try

[julianoes]

Yeah, sorry. I hadn't made the pull request because there were going to be changes to CubeRed and I didn't want to push something that was going to change anyway.

I'll have a look at what/how you did it. It might be better!

[HTRamsey]

I wouldn't hold your breath on that