Handle renames and/or detect whether the crate is being built or checked

[ghost]

I'm not entirely sure if there is a universally sane way to handle this, but I'm seeing a lot of spurious gdns files being made during development when I try various type names, since I've configured rust-analyzer to check the project on save. The easiest way, I believe, would be adding an option to automatically delete orphaned gdns files in the output directory. This would of course destroy any custom changes made on the files, so it's not ideal, but it should suffice for simple use cases.

Another approach might be somehow detecting whether the crate is actually being built with a cargo build command, if possible, and skip generation if not. An option might also be added for this, although I doubt it'll be very useful to opt out of this.