Feature request: Custom dimensions and refunits

[yaccos]

Dear maintainers of DynamicQuantities,

I see that this package has the option of defining custom units by the macro @register_unit. However, I would like to have equivalents of Unitful's @dimension and @refunit. Is this possible to do with DyanamicQuantities?

[MilesCranmer]

It's a little bit different in DynamicQuantities because all the dimensions are tracked. So the closest equivalent is defining a custom dimensions space using a struct: https://ai.damtp.cam.ac.uk/dynamicquantities/dev/examples/#3.-Using-dimensional-angles where you can add or remove dimensions from processing.