MMU: Set PAUSED_FOR_USER state on MMU error screen

[gudnimg]

Setting this state notifies PrusaLink/PrusaConnect that the printer is waiting for user input (attention).

Resolves #4470

Change in memory:
Flash: +12 bytes
SRAM: 0 bytes

[github-actions]

All values in bytes. Δ Delta to base

Target	ΔFlash	ΔSRAM	Used Flash	Used SRAM	Free Flash	Free SRAM
MK3S_MULTILANG	12	0	245922	5633	8030	2559
MK3_MULTILANG	12	0	245206	5642	8746	2550

[firetech]

I built a test firmware with this cherry-picked on top of 3.13.2 (7aff0db), and did some quick tests with induced failures, both from idle state (Load to nozzle) and from within a print. Seems to work. :)

[gudnimg]

I did a few tests on my side:

• ✅ M600 with MMU (Tested the new filament change screen in 3.13.2)
• ❌ SELECTOR CANNOT HOME when Idle. When the firmware is running the top-level loop() the status is reset, I rather not touch this code.

[3d-gussner]

Tested with MK404, PrusaLink 0.72.0 and PrusaConnect

Test Steps:

1. Start MK404 with MMU
2. Start prusalink -s /tmp/simavr-uart0 -l prusa.link.serial.serial_adapter=DEBUG -i -f
3. In PrusaConnect start SD print
4. During print press "F" in MK404 to manually set FINDA
5. Wait for MMU error
6. Check in PrusaLink and PrusaConnect the printer state

Before:
PrusaLink and PrusaConnect don't detect any issue and printer state says printing

With this PR:
PruasLink and PrusaConncet change state to Attention