Add Raspberry Pi Pico platform #1991

Job	Run time
Check c99 compilation	21s
Check codebase format with clang-format	3s
Test examples without router	18s
Run unit tests on ubuntu-latest	27s
Build raweth transport on ubuntu-latest	15s
Check compilation with unstable API	14s
Build Zenoh from source	5m 25s
Build and test in single thread on ubuntu-latest	35s
Test attachments	38s
Modular build on ubuntu-latest (1, 1, 1, 1)	39s
Test multicast and unicast fragmentation	47s
Modular build on ubuntu-latest (1, 1, 1, 0)	41s
Test examples memory leak	1m 4s
Modular build on ubuntu-latest (1, 1, 0, 1)	39s
Modular build on ubuntu-latest (1, 1, 0, 0)	40s
Modular build on ubuntu-latest (1, 0, 1, 1)	41s
Modular build on ubuntu-latest (1, 0, 1, 0)	56s
Modular build on ubuntu-latest (1, 0, 0, 1)	36s
Modular build on ubuntu-latest (1, 0, 0, 0)	37s
Modular build on ubuntu-latest (0, 1, 1, 1)	31s
Modular build on ubuntu-latest (0, 1, 1, 0)	23s
Modular build on ubuntu-latest (0, 1, 0, 1)	26s
Modular build on ubuntu-latest (0, 1, 0, 0)	21s
Modular build on ubuntu-latest (0, 0, 1, 1)	36s
Modular build on ubuntu-latest (0, 0, 1, 0)	27s
Modular build on ubuntu-latest (0, 0, 0, 1)	33s
Modular build on ubuntu-latest (0, 0, 0, 0)	22s
	19m 15s

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