Add a new env var UV_LOOP_ENABLE_IO_URING_SQPOLL

[ronag]

libuv disables SQPOLL by default and leaves it to the user/admin to enable/disable. However, I believe it's currently not possible to do this in node.

We should add a check for a UV_LOOP_ENABLE_IO_URING_SQPOLL env flag and call uv_loop_configure with the libuv flag UV_LOOP_ENABLE_IO_URING_SQPOLL.

Refs: libuv/libuv#4492

[ronag]

Related to our the current UV_USE_IO_URING env var.

[bnoordhuis]

Not your var, our var :-)

Suggestion: prefix with NODE_ instead of UV_

[ronag]

@bnoordhuis wouldn't it be easier if libuv exposed this as some kind of UV_LOOP_ENABLE_IO_URING_SQPOLL_BY_DEFAULT env var?

[bnoordhuis]

Maybe I'll add that someday but I'm in no particular rush. I don't really like ambient state like environment variables affecting the behavior of a library (programs? okay. libraries? not so much)