Add Raspberry Pi Pico platform #1972

Job	Run time
Run unit tests on ubuntu-latest	35s
Check c99 compilation	13s
Check codebase format with clang-format	4s
Test examples without router	21s
Build raweth transport on ubuntu-latest	12s
Check compilation with unstable API	14s
Build Zenoh from source	5m 45s
Test attachments	37s
Modular build on ubuntu-latest (1, 1, 1, 1)	39s
Test examples memory leak	1m 6s
Modular build on ubuntu-latest (1, 1, 1, 0)	43s
Test multicast and unicast fragmentation	43s
Modular build on ubuntu-latest (1, 1, 0, 1)	39s
Build and test in single thread on ubuntu-latest	37s
Modular build on ubuntu-latest (1, 1, 0, 0)	37s
Modular build on ubuntu-latest (1, 0, 1, 1)	40s
Modular build on ubuntu-latest (1, 0, 1, 0)	37s
Modular build on ubuntu-latest (1, 0, 0, 1)	39s
Modular build on ubuntu-latest (1, 0, 0, 0)	35s
Modular build on ubuntu-latest (0, 1, 1, 1)	30s
Modular build on ubuntu-latest (0, 1, 1, 0)	28s
Modular build on ubuntu-latest (0, 1, 0, 1)	25s
Modular build on ubuntu-latest (0, 1, 0, 0)	32s
Modular build on ubuntu-latest (0, 0, 1, 1)	31s
Modular build on ubuntu-latest (0, 0, 1, 0)	23s
Modular build on ubuntu-latest (0, 0, 0, 1)	27s
Modular build on ubuntu-latest (0, 0, 0, 0)	22s
	19m 14s

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