Experimental message passing based pool implementation #2831

Job	Run time
armhf Linux glibc	27m 33s
aarch64 Linux glibc	21m 40s
arm64 Apple Darwin	13m 9s
arm Linux glibc	27m 50s
riscv64 Linux glibc	23m 22s
Lint bash, docker, markdown, and yaml	1m 38s
Validate GNU Docker image builds	30s
Validate GNU Docker release image builds	43s
Validate musl Docker image builds	19s
Validate musl Docker release image builds	18s
Validate Windows Docker image builds	11m 49s
Validate Windows Docker release image builds	8m 55s
Verify CHANGELOG is valid	8s
x86-64 Linux glibc	20m 54s
x86-64 Apple Darwin	26m 6s
x86-64 Linux musl	23m 28s
x86-64 Windows MSVC	38m 47s
use dtrace	21m 12s
use pool_memalign	24m 2s
use runtimestats	22m 22s
use pool_message_passing	4m 59s
	5h 19m 44s

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