micro tasks: run micro tasks on isolate every 1 millisecond

[krichprollsch]

This PR exposes runMicrotasks and pumpMessageLoop.
It also run runMicrotasks every millisecond using timeouts.

I'm not sure if it's correct to implement this loop using timeout to run the runMicrotasks.
pro: it is handled by zig js runtime transparently
con: the caller doesn't control the delay between the runs

Fix #56

[karlseguin]

Is this check necessary? I don't think there's an harm in continuously executing this, even if the "ctx_id" has been increased.

[krichprollsch]

This is a good point. My PR doesn't work if the browser removes the page and reset the loop.

My idea was: the loop has a longer lifetime than the isolate. That's why I wanted to use the ctx_id to avoid callbacks after any env deinit.

Currently we have:

• main creates the loop
• a new conn arrives
• we create and init the CDP which init the browser
• eventually a browser context is created which create a brower's session which init a js env => the runMicrotasks loop starts
• eventually the session's removepage is called which reset the loop's context id => microtasks loop stops, we don't want that.
• envetually the browser context is discarded along with the session and the env => the microtasks loop should stop
• the session, the env, the browser and the cdp conn are deinit => the microtasks loop should stop

=> I don't want a future timeout is called after the env deinit

But the current ctx_id doesn't match to what I want for running micro tasks.

[krichprollsch]

I introduced 2 differents ctx_id in the loop: one for the js callbacks and another for the zig one.
This is not perfect b/c we could have other zig callback independent lifetimes... But it unblocks me for now.
I haven't found a better way to handle that for now.