Updating watchdog service rate

[ryan-summers]

This PR increases the watchdog interval from 2s -> 4s to account for 1.8s potential in the idle task due to ARP timeouts of the W5500. Additionally, this simplifies the fan self-test to not test low-speed operation of the fans to reduce startup time. Finally, a mutex is shorted in the idle task to make other tasks more responsive.

TODO:

• Test debug and release binaries on hardware for watchdogs
• Measure watchdog service interval

This PR fixes #94
This PR fixes #110

[jordens]

Moving to raw sockets for the w5500 and smoltcp on top of that presumably will also help once we can do that.

[ryan-summers]

I created a test binary that flashed LED3 on the booster mainboard whenever the watchdog was serviced. I confirmed that during MQTT-disconnect, the service interval was slightly below 2s, but very close to it, so it's possible we may have been exceeding it previously. These changes should help alleviate any task stackup-related issues.

Additionally, I ran firmware for ~53 minutes continuously and didn't observe any watchdogs/resets. We'll have to observe stability going forward after these changes.