retainClear

pub fn retainClear(self: *Self, token: retainToken) void {
            self.retain_map.lockPointers();
            defer self.retain_map.unlockPointers();
            var it = self.retain_map.iterator();
            while (it.next()) |entry| {
                if (entry.value_ptr.* == token) {
                    self.retain_map.removeByPtr(entry.key_ptr);
                }
            }
        }