refactor(ram_monitor): ros2 port #54

Job	Run time
diagnostic_aggregator on humble	5m 8s
diagnostic_aggregator on iron	4m 24s
diagnostic_aggregator on rolling	2m 31s
diagnostic_common_diagnostics on humble	3m 35s
diagnostic_common_diagnostics on iron	3m 6s
diagnostic_common_diagnostics on rolling	2m 34s
diagnostic_updater on humble	4m 11s
diagnostic_updater on iron	4m 17s
diagnostic_updater on rolling	2m 22s
self_test on humble	3m 47s
self_test on iron	3m 54s
self_test on rolling	2m 13s
	42m 2s

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