GH-5807 Recover LMDB readers safely when maxreaders is full #7087

Job	Run time
copyright-check	32s
formatting-and-quick-compile	2m 15s
integration-tests	18m 40s
slow-tests	31m 24s
frontend-unit-tests	29s
package-assembly	4m 37s
e2e	7m 1s
build (11)	24m 19s
build (25)	21m 57s
compile	4m 53s
	1h 56m 7s

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