Merge branch 'develop' of github.com:futureverse/future into develop #401

Job	Run time
future.plan=cluster	2m 58s
future.plan=multicore	2m 19s
future.plan=multisession	2m 56s
future.plan=sequential	2m 27s
future.plan=future.batchtools::batchtools_local	4m 5s
future.plan=future.batchtools::batchtools_bash	4m 2s
future.plan=future.callr::callr	4m 2s
	22m 49s

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