core: prevent scope parent-chain cycles when reusing pooled frames

- Scope.resetForReuse: fully detach before re-parenting (clear state, parent=null, new frameId), then validate with ensureNoCycle and assign parent/args/pos/thisObj
- ScopePool.borrow (JVM/Android/JS/Native/Wasm): defensive fallback to fresh Scope allocation if resetForReuse detects a cycle
- docs: add docs/fix-scope-parent-cycle.md describing the change and expectations
- test: add ScopeCycleRegressionTest to ensure instance method call pattern does not crash and returns "ok"

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt

@@ -302,11 +302,9 @@ open class Scope(
      * Clears locals and slots, assigns new frameId, and sets parent/args/pos/thisObj.
      */
     fun resetForReuse(parent: Scope?, args: Arguments, pos: Pos, thisObj: Obj) {
-        ensureNoCycle(parent)
-        this.parent = parent
-        this.args = args
-        this.pos = pos
-        this.thisObj = thisObj
+        // Fully detach from any previous chain/state first to avoid residual ancestry
+        // that could interact badly with the new parent and produce a cycle.
+        this.parent = null
         this.skipScopeCreation = false
         // fresh identity for PIC caches
         this.frameId = nextFrameId()
@@ -315,6 +313,12 @@ open class Scope(
         slots.clear()
         nameToSlot.clear()
         localBindings.clear()
+        // Now safe to validate and re-parent
+        ensureNoCycle(parent)
+        this.parent = parent
+        this.args = args
+        this.pos = pos
+        this.thisObj = thisObj
         // Pre-size local slots for upcoming parameter assignment where possible
         reserveLocalCapacity(args.list.size + 4)
     }