Add support for pinning actors to a dedicated scheduler thread #2747

Job	Run time
Validate musl Docker image builds	20s
Validate GNU Docker image builds	41s
Lint bash, docker, markdown, and yaml	1m 40s
Validate musl Docker release image builds	26s
Validate Windows Docker image builds	2m 2s
Validate GNU Docker release image builds	39s
aarch64 Linux glibc	6h 0m 2s
arm64 Apple Darwin	36m 55s
armhf Linux glibc	6h 0m 3s
arm Linux glibc	6h 0m 3s
riscv64 Linux glibc	6h 0m 2s
Validate Windows Docker release image builds	1m 38s
Verify CHANGELOG is valid	6s
x86-64 Linux glibc	6h 0m 0s
x86-64 Apple Darwin	1h 17m 19s
x86-64 Linux musl	6h 0m 0s
x86-64 Windows MSVC	38m 6s
use ${{ matrix.directives }}	0s
	1d 14h 40m 2s

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