From the first glance it seems like Spine provides their libraries in source format (under non open source license) with pure C++, C# and TS implementations that don't depend on binary blobs (at least it seemed like it). You can find it here https://github.com/esotericsoftware/spine-runtimes . Even if C++ version is not safe, C# and TS versions are probably fine and, and the license mentions creating derivative works (assuming you follow the Editor license terms and some of invovled parties have an editor license) so you are probably allowed to create modified library which processes the files safely.