Consider using custom canvas server

[ehne]

Currently PyNode Next uses the default canvas server, this has some issues in how it understands where files are and what to load. This results in the slightly odd looking code in core:

base_path = os.path.relpath(__file__)
self.custom_ui = f"{Path(base_path).parent}/ui.html"

This is due to how if you use a custom html file (like PyNode Next does) it switches to using a relative file handler, rather than an absolute one. Hence the relpath call.

This problem results in the unfortunate side effect that we cannot package PyNode Next for PyPi, as it is unable to find a suitable relative path to work with. Meaning that users have to download a new copy of PyNode Next for every project (or move the same copy between projects). This also means that when uploading work done with PyNode Next, it will also include the PyNode Next source files. (this is both good and bad. good because it means that whatever version of PyNode Next is used in a project will be the same with the same project on a different machine, but bad for the reasons outlined before).

If we were to use a custom implementation of AlgorithmX's CanvasServer class, we would have more control over what path could be loaded. In theory we should just be able to replace the init function of CanvasServer.