Add rb_ec_close function to manage execution context cleanup. (ruby#15253)

Author: samuel-williams-shopify

cont.c

@@ -2907,6 +2907,7 @@ void
 rb_fiber_close(rb_fiber_t *fiber)
 {
     fiber_status_set(fiber, FIBER_TERMINATED);
+    rb_ec_close(&fiber->cont.saved_ec);
 }
 
 static void

vm.c

@@ -3890,6 +3890,13 @@ rb_ec_clear_vm_stack(rb_execution_context_t *ec)
     rb_ec_set_vm_stack(ec, NULL, 0);
 }
 
+void
+rb_ec_close(rb_execution_context_t *ec)
+{
+    // Fiber storage is not accessible from outside the running fiber, so it is safe to clear it here.
+    ec->storage = Qnil;
+}
+
 static void
 th_init(rb_thread_t *th, VALUE self, rb_vm_t *vm)
 {

vm_core.h

@@ -1104,6 +1104,10 @@ void rb_ec_initialize_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t
 // @param ec the execution context to update.
 void rb_ec_clear_vm_stack(rb_execution_context_t *ec);
 
+// Close an execution context and free related resources that are no longer needed.
+// @param ec the execution context to close.
+void rb_ec_close(rb_execution_context_t *ec);
+
 struct rb_ext_config {
     bool ractor_safe;
 };