Add Raspberry Pi Pico platform #1986

Job	Run time
Check codebase format with clang-format	4s
Build raweth transport on ubuntu-latest	16s
Run unit tests on ubuntu-latest	1m 47s
Check c99 compilation	14s
Test examples without router	47s
Check compilation with unstable API	20s
Build Zenoh from source	5m 46s
Build and test in single thread on ubuntu-latest	39s
Test attachments	38s
Test examples memory leak	1m 20s
Test multicast and unicast fragmentation	43s
Modular build on ubuntu-latest (1, 1, 1, 1)	1m 12s
Modular build on ubuntu-latest (1, 1, 1, 0)	38s
Modular build on ubuntu-latest (1, 1, 0, 1)	45s
Modular build on ubuntu-latest (1, 1, 0, 0)	1m 4s
Modular build on ubuntu-latest (1, 0, 1, 1)	45s
Modular build on ubuntu-latest (1, 0, 1, 0)	45s
Modular build on ubuntu-latest (1, 0, 0, 1)	42s
Modular build on ubuntu-latest (1, 0, 0, 0)	43s
Modular build on ubuntu-latest (0, 1, 1, 1)	47s
Modular build on ubuntu-latest (0, 1, 1, 0)	27s
Modular build on ubuntu-latest (0, 1, 0, 1)	45s
Modular build on ubuntu-latest (0, 1, 0, 0)	1m 0s
Modular build on ubuntu-latest (0, 0, 1, 1)	1m 1s
Modular build on ubuntu-latest (0, 0, 1, 0)	32s
Modular build on ubuntu-latest (0, 0, 0, 1)	29s
Modular build on ubuntu-latest (0, 0, 0, 0)	26s
	24m 35s

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