new implementations for --gc:orc (#14121)

* cycle collector: new implementation
* cycle collector: make self-adaptive based on its previous effectiveness
* cycle collector: added Lins's jump stack to improve traversal from 3*N to 2*N
* cycle collector: make tests green
* API extensions and bugfixes
* code cleanup and use --gc:orc for tasyncawait

tests/arc/tasyncawait.nim

@@ -1,6 +1,6 @@
 discard """
   outputsub: "result: 5000"
-  cmd: "nim c --gc:arc $file"
+  cmd: "nim c --gc:orc $file"
 """
 
 import asyncdispatch, asyncnet, nativesockets, net, strutils, os
@@ -71,4 +71,5 @@ main()
 
 assert msgCount == swarmSize * messagesToSend
 echo "result: ", msgCount
+GC_fullCollect()
 echo "memory: ", formatSize(getOccupiedMem() - mem)