Autoload encodings on the main ractor #290

Job	Run time
cargo test	34s
make (check, --enable-yjit, --yjit)	6m 8s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx --yjit-code-gc, -T --yj...	18m 52s
YJIT macOS Arm64 result	3s
	25m 37s

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