fix: propagate aborted fiber error check before call and unwind caller chain in runtimeError

Move the aborted fiber check in runFiber to execute before the "already called" check, ensuring a clear error message for aborted fibers. In runtimeError, replace the single caller unhook with a loop that walks the fiber chain, preserving the callerIsTrying flag and only unhooking fibers until a try-catch boundary is found, enabling proper error propagation through nested fiber calls. Add test cases for one and two levels of nested fiber try calls.

test/core/fiber/try.wren

@@ -8,3 +8,34 @@ System.print(fiber.try())
 // expect: before
 // expect: Bool does not implement 'unknownMethod'.
 System.print("after try") // expect: after try
+
+var fiber2 = Fiber.new {
+  var fiberInner = Fiber.new {
+    System.print("before")
+    true.unknownMethod
+    System.print("after")
+  }
+  fiberInner.call()
+}
+
+System.print(fiber2.try())
+// expect: before
+// expect: Bool does not implement 'unknownMethod'.
+System.print("after try") // expect: after try
+
+var fiber3 = Fiber.new {
+  var fiberInner = Fiber.new {
+    var fiberInnerInner = Fiber.new {
+      System.print("before")
+      true.unknownMethod
+      System.print("after")
+    }
+    fiberInnerInner.call()
+  }
+  fiberInner.call()
+}
+
+System.print(fiber3.try())
+// expect: before
+// expect: Bool does not implement 'unknownMethod'.
+System.print("after try") // expect: after try