Add Raspberry Pi Pico platform #1987

Job	Run time
Check c99 compilation	22s
Check codebase format with clang-format	3s
Build raweth transport on ubuntu-latest	13s
Run unit tests on ubuntu-latest	34s
Check compilation with unstable API	12s
Build Zenoh from source	5m 35s
Test examples without router	20s
Build and test in single thread on ubuntu-latest	38s
Test attachments	38s
Test multicast and unicast fragmentation	48s
Test examples memory leak	1m 5s
Modular build on ubuntu-latest (1, 1, 1, 1)	40s
Modular build on ubuntu-latest (1, 1, 1, 0)	38s
Modular build on ubuntu-latest (1, 1, 0, 1)	40s
Modular build on ubuntu-latest (1, 1, 0, 0)	38s
Modular build on ubuntu-latest (1, 0, 1, 1)	48s
Modular build on ubuntu-latest (1, 0, 1, 0)	36s
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)	41s
Modular build on ubuntu-latest (0, 1, 0, 1)	27s
Modular build on ubuntu-latest (0, 1, 0, 0)	26s
Modular build on ubuntu-latest (0, 0, 1, 1)	27s
Modular build on ubuntu-latest (0, 0, 1, 0)	23s
Modular build on ubuntu-latest (0, 0, 0, 1)	28s
Modular build on ubuntu-latest (0, 0, 0, 0)	23s
	19m 27s

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