Fix issue with long wait for passed timer [bugfix] (#12221)

* Fix issue with long wait for passed timer [bugfix]

This fixes a small issue where a timer that had been completed while
code executed would still wait for more events before being considered
completed. This would in some scenarios incur a 500ms delay to the
completion of a timer.

* Refactor logic into

* Add test case based on original issue

* Use longer timeouts to be more lenient in checking

* Revert to short timeouts, but widen the accepted range

* Widen accepted range further, it is meant to check for a 500ms delay after all

* Increase poll timeout to make it easier to detect mistakes

lib/pure/asyncdispatch.nim

@@ -210,7 +210,12 @@ proc processPendingCallbacks(p: PDispatcherBase; didSomeWork: var bool) =
     cb()
     didSomeWork = true
 
-proc adjustTimeout(pollTimeout: int, nextTimer: Option[int]): int {.inline.} =
+proc adjustTimeout(
+  p: PDispatcherBase, pollTimeout: int, nextTimer: Option[int]
+): int {.inline.} =
+  if p.callbacks.len != 0:
+    return 0
+
   if nextTimer.isNone() or pollTimeout == -1:
     return pollTimeout
 
@@ -324,7 +329,7 @@ when defined(windows) or defined(nimdoc):
 
     result = false
     let nextTimer = processTimers(p, result)
-    let at = adjustTimeout(timeout, nextTimer)
+    let at = adjustTimeout(p, timeout, nextTimer)
     var llTimeout =
       if at == -1: winlean.INFINITE
       else: at.int32
@@ -1284,7 +1289,8 @@ else:
     result = false
     var keys: array[64, ReadyKey]
     let nextTimer = processTimers(p, result)
-    var count = p.selector.selectInto(adjustTimeout(timeout, nextTimer), keys)
+    var count =
+      p.selector.selectInto(adjustTimeout(p, timeout, nextTimer), keys)
     for i in 0..<count:
       let fd = keys[i].fd.AsyncFD
       let events = keys[i].events