Add Raspberry Pi Pico platform #2070

Job	Run time
Check c99 compilation	18s
Check codebase format with clang-format	5s
Test examples without router	25s
Build raweth transport on ubuntu-latest	21s
Check compilation with unstable API	19s
Run unit tests on ubuntu-latest	1m 1s
Build Zenoh from source	5m 45s
Test multicast and unicast fragmentation	48s
Test examples memory leak	1m 15s
Test attachments	42s
Modular build on ubuntu-latest (1, 1, 1, 1)	46s
Build and test in single thread on ubuntu-latest	1m 31s
Modular build on ubuntu-latest (1, 1, 1, 0)	44s
Modular build on ubuntu-latest (1, 1, 0, 1)	45s
Modular build on ubuntu-latest (1, 1, 0, 0)	46s
Modular build on ubuntu-latest (1, 0, 1, 1)	45s
Modular build on ubuntu-latest (1, 0, 1, 0)	39s
Modular build on ubuntu-latest (1, 0, 0, 1)	45s
Modular build on ubuntu-latest (1, 0, 0, 0)	41s
Modular build on ubuntu-latest (0, 1, 1, 1)	31s
Modular build on ubuntu-latest (0, 1, 1, 0)	27s
Modular build on ubuntu-latest (0, 1, 0, 1)	31s
Modular build on ubuntu-latest (0, 1, 0, 0)	27s
Modular build on ubuntu-latest (0, 0, 1, 1)	44s
Modular build on ubuntu-latest (0, 0, 1, 0)	30s
Modular build on ubuntu-latest (0, 0, 0, 1)	36s
Modular build on ubuntu-latest (0, 0, 0, 0)	29s
	22m 36s

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