fixes #23825; Busy wait on waitid, sleeping at regular intervals (#23826)

Addresses #23825 by using the approaching described in
https://github.com/nim-lang/Nim/pull/23743#issuecomment-2199523110.

This takes the approach from Python's `subprocess` library which calls
`waitid` in loop, while sleeping at regular intervals.

CC @alex65536

tests/osproc/twaitforexit.nim

@@ -15,4 +15,19 @@ block: # bug #5091
             discard
 
         # check that we don't have to wait msWait milliseconds
-        doAssert(getTime() <  atStart + milliseconds(msWait))
+        doAssert(getTime() <  atStart + milliseconds(msWait))
+
+block: # bug #23825
+    var thr: array[0..99, Thread[int]]
+
+    proc threadFunc(i: int) {.thread.} =
+        let sleepTime = float(i) / float(thr.len + 1)
+        doAssert sleepTime < 1.0
+        let p = startProcess("sleep", workingDir = "", args = @[$sleepTime], options = {poUsePath, poParentStreams})
+        # timeout = 1_000_000 seconds ~= 278 hours ~= 11.5 days
+        doAssert p.waitForExit(timeout=1_000_000_000) == 0
+
+    for i in low(thr)..high(thr):
+        createThread(thr[i], threadFunc, i)
+
+    joinThreads(thr)