Import associated `<-` symbols (e.g. like `names<-`) with mod::use

Is it possible, in the new syntax, to make mod::use(raster[crs]) also attach crs<-? I don't think klmr/modules, wahani/modules, or smbache/import can currently do anything like this.

Opening new issue as instructed in #129.

Start by reading the new mod::use syntax described in the issue and the context from #129. Determine whether importing associated `<-` symbols such as `crs<-` is intended, and document the required behavior and scope before considering an implementation.

Written by the indexing model from the issue text.