SNMP: Replace mib_tree_entry struct with MEMPROXY class #1826

Job	Run time
functionality-tests	20m 49s
source-maintenance-tests	4m 7s
build-tests(ubuntu-24.04,gcc,default)	7m 41s
build-tests(ubuntu-24.04,gcc,minimal)	5m 1s
build-tests(ubuntu-24.04,gcc,maximus)	8m 26s
build-tests(ubuntu-24.04,clang,maximus)	10m 16s
build-tests(ubuntu-24.04,clang,default)	8m 55s
CodeQL-tests	26m 53s
build-tests(ubuntu-24.04,clang,minimal)	8m 1s
	1h 40m 9s

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