Add Raspberry Pi Pico platform #1990

Job	Run time
Check codebase format with clang-format	4s
Run unit tests on ubuntu-latest	34s
Check c99 compilation	15s
Test examples without router	29s
Build raweth transport on ubuntu-latest	11s
Check compilation with unstable API	15s
Build Zenoh from source	5m 31s
Build and test in single thread on ubuntu-latest	32s
Modular build on ubuntu-latest (1, 1, 1, 1)	44s
Test multicast and unicast fragmentation	1m 5s
Modular build on ubuntu-latest (1, 1, 1, 0)	35s
Test attachments	39s
Test examples memory leak	1m 15s
Modular build on ubuntu-latest (1, 1, 0, 1)	49s
Modular build on ubuntu-latest (1, 1, 0, 0)	36s
Modular build on ubuntu-latest (1, 0, 1, 1)	40s
Modular build on ubuntu-latest (1, 0, 1, 0)	32s
Modular build on ubuntu-latest (1, 0, 0, 1)	40s
Modular build on ubuntu-latest (1, 0, 0, 0)	36s
Modular build on ubuntu-latest (0, 1, 1, 1)	25s
Modular build on ubuntu-latest (0, 1, 1, 0)	24s
Modular build on ubuntu-latest (0, 1, 0, 1)	27s
Modular build on ubuntu-latest (0, 1, 0, 0)	31s
Modular build on ubuntu-latest (0, 0, 1, 1)	29s
Modular build on ubuntu-latest (0, 0, 1, 0)	22s
Modular build on ubuntu-latest (0, 0, 0, 1)	25s
Modular build on ubuntu-latest (0, 0, 0, 0)	22s
	19m 27s

Provide feedback