Objects not destroyed at the end of each round

[gitchly]

Not explicitly destroying/clearing objects after each round may lead to too much memory usage. The same goes for undo/redo, when a user has a redo queue but draws, the redo queue is not correctly destroyed.

This is especially apparent in the shader-renderer branch, where ShaderPath objects store multiple buffers and other values that may not get cleaned up correctly.

[gitchly]

Objects now have their dispose() function called during canvas.clear():

https://github.com/darkrilin/drawry/blob/cc47542e4ca4e5240bd900f8f0c0744e2c674e47/static/js/fabric-regl.js#L24-L27

However, the issue will remain open until a dispose() function is implemented for each of the classes.