[radio] refactor `Radio::Statistics` (#10961) #122

Job	Run time
channel-manager-csl	3m 24s
expects	31m 47s
packet-verification-1-1-on-1-4	14m 14s
packet-verification-low-power	10m 4s
thread-1-4-gcc-m32	11m 5s
thread-1-4-posix	9m 40s
thread-1-4-gcc-m64	11m 32s
thread-1-4-clang-m32	9m 20s
thread-1-4-clang-m64	9m 50s
upload-coverage	0s
	1h 50m 56s

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