rp2040 baremetal threading

[gundralaa]

using the mutex and queue primitives from the pico-sdk, basic baremetal threading on the rp2040 platform is implemented to utilize both cores.

• each core runs one worker
• the queue is used as an analog for condition variables
• basic smoke test using the example here

TODO

• ideally a lower level primitive is used instead of the queue for performance. the spinlock resource could definitely be leveraged to implement a basic condition variable with the mutex. some work already done here
• testing physical actions / interrupt coexistence with the threaded runtime
• running and verifying all threaded runtime tests.
• verify other schedulers