Add `rb_ec_close` function to manage execution context cleanup. (#15253) #631

Job	Run time
make (yjit-bindgen, To fix: use patch in logs, --with-gcc=clang-14 --enable-yjit=dev, /usr/lib/ll...	5m 15s
cargo clippy	39s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx --yjit-code-gc, -T --yj...	18m 58s
cargo test	51s
make (check, RUSTC='rustc +1.58.0', 1.58.0)	10m 26s
make (test-bundled-gems, --enable-yjit=dev)	24m 30s
make (check, --enable-yjit=dev)	12m 53s
YJIT Ubuntu result	4s
	1h 13m 36s

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