refactor(time): refactor delay with input checking

Previously, there were three low-level delay entry points

- os_delay(ms, ignoreinput=true): sleep for ms, only break on got_int

- os_delay(ms, ignoreinput=false): sleep for ms, break on any key input
  os_microdelay(us, false): equivalent, but in μs (not directly called)

- os_microdelay(us, true): sleep for μs, never break.

The implementation of the latter two both used uv_cond_timedwait()
This could have been for two reasons:
 1. allow another thread to "interrupt" the wait
 2. uv_cond_timedwait() has higher resolution than uv_sleep()

However we (1) never used the first, even when TUI was a thread, and
(2) nowhere in the codebase are we using μs resolution, it is always a ms
multiplied with 1000.

In addition, os_delay(ms, false) would completely block the thread for
100ms intervals and in between check for input. This is not how event handling
is done alound here.

Therefore:

Replace the implementation of os_delay(ms, false) to use
LOOP_PROCESS_EVENTS_UNTIL which does a proper epoll wait with a timeout,
instead of the 100ms timer panic.

Replace os_microdelay(us, false) with a direct wrapper of uv_sleep.

test/unit/helpers.lua

@@ -97,7 +97,6 @@ local init = only_separate(function()
   for _, c in ipairs(child_calls_init) do
     c.func(unpack(c.args))
   end
-  libnvim.time_init()
   libnvim.fs_init()
   libnvim.event_init()
   libnvim.early_init(nil)