Add nanopb as an external submodule #1301

Job	Run time
Windows	8m 4s
macOS 14 (arm64/M1/M2)	2m 55s
Analyze (CodeQL) (cpp)	12m 34s
Debian Bullseye (x86_64)	1m 28s
macOS 13 (x64)	5m 56s
Analyze (CodeQL) (javascript)	2m 24s
Debian Bullseye (ARM 32-bit Raspberry Pi OS)	7m 12s
Debian Bullseye (ARM 64-bit Raspberry Pi OS)	6m 36s
Debian Bookworm (x86_64)	1m 59s
Ubuntu 22.04 LTS (x86_64)	1m 26s
Ubuntu 24.04 LTS (x86_64)	1m 43s
Debian Bookworm (ARM 32-bit Raspberry Pi OS)	7m 46s
Debian Bookworm (ARM 64-bit Raspberry Pi OS)	7m 28s
Fedora 40 (x86_64)	3m 32s
Arch Linux (x86_64)	7m 29s
Publish Releases	0s
	1h 18m 32s

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