refactor(ram_monitor): ros2 port #49

Job	Run time
diagnostic_aggregator on humble	3m 15s
diagnostic_aggregator on iron	4m 9s
diagnostic_aggregator on rolling	2m 7s
diagnostic_common_diagnostics on humble	3m 46s
diagnostic_common_diagnostics on iron	3m 21s
diagnostic_common_diagnostics on rolling	2m 21s
diagnostic_updater on humble	3m 19s
diagnostic_updater on iron	3m 4s
diagnostic_updater on rolling	2m 28s
self_test on humble	3m 24s
self_test on iron	3m 22s
self_test on rolling	1m 48s
	36m 24s

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