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

lib/system/cyclebreaker.nim

@@ -52,6 +52,8 @@ That seems acceptable, no leak is produced. This implies that the standard
 depth-first traversal suffices.
 
 ]#
+
+type PT = ptr pointer
 include cellseqs_v2
 
 const