Experimental message passing based pool implementation #2830

Job	Run time
Lint bash, docker, markdown, and yaml	1m 45s
Validate GNU Docker image builds	45s
Validate musl Docker image builds	21s
Validate Windows Docker image builds	10m 16s
arm Linux glibc	1h 23m 18s
riscv64 Linux glibc	1h 18m 19s
Validate GNU Docker release image builds	35s
Validate musl Docker release image builds	22s
Validate Windows Docker release image builds	10m 31s
Verify CHANGELOG is valid	12s
x86-64 Linux glibc	1h 15m 10s
aarch64 Linux glibc	1h 15m 12s
x86-64 Linux musl	1h 55m 32s
arm64 Apple Darwin	40m 50s
armhf Linux glibc	1h 22m 24s
x86-64 Apple Darwin	1h 26m 26s
x86-64 Windows MSVC	1h 10m 6s
use dtrace	20m 44s
use pool_memalign	24m 25s
use runtimestats	21m 23s
use pool_message_passing	37s
	13h 19m 13s

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