Fix clearTimeout and linux timeout

[zhuzilin]

fix #1135

It seems that there were lots of bugs for setTimeout/setInterval. So I'll try to clarify what I'm trying to do in this PR, in case it introduces some new bugs :p

The rationale is, for each timeout event, the vm.active_tasks will be added twice:

• one in event loop, just like any other IOTask (IOTask.createOnJSThread);
• the other in Timer.set, which is an additional count for timer.

active_tasks will prevent bun from exit: bun will loop to wait until active_task is zero.

And correpsond to the 2 add, there will be 2 minus:

• one in event loop, when a task is finished, event loop will minus 1 to active_task
• the other in Timer, when a timer is triggered, and it won't happen again, active_task need to be -|= 1ed.

The reason timer events need 2 adds instead of 1 is that, when a timer event will repeat, we can just not do the second minus and keep bun alive.

There were several problem with the origin implementation.

• when clear the timeout (clearTimer), we should do -|= 2, so that bun could exit immediately. Instead, currently it only set timer.cancelled to true.
• no need to add to active_task when repeating, not minusing is good enough, otherwise, the setInterval cannot be cancelled.

And in this pr, I changed the code into:

• active_tasks -|= 2 in clearTimer
• don't active_tasks +|= 1 for repeat timer
• don't active_tasks -|= 1 in clear, as the timer may be canceled already.

Also, for linux timeout, we should not set the count field in io_uring_prep_timeout, as it has a special function. For more information, please check: axboe/liburing#232

Thank you for your time on this PR :)

[Jarred-Sumner]

This is great! Thank you.