Split out our Rust `crates` folder into groups

[emilk]

We're building more and more "script"-like Rust crates.

These should be in their own folder (e.g. crates/scripts), or be unified under one binary (xtask style).

Similarly, perhaps we should put all space views into their own folder, etc.

Group similarly to the schematic in ARCHITECTURE.md

[emilk]

One thing I've been considering is splitting re_format. Most of what it does is very general stuff (formatting numbers), but it also does some very high-level stuff (formatting arrow data, and stuff in re_types_core).

I think we need a simple crate for just formatting numbers and the like, and either move the high level stuff out into the various crates they touch (e.g. move formatting of re_types_core to re_types_core), or have a high-level formatting crate.

I'd also like to have some of the number formatting available for egui_plots, so perhaps it makes sense to move the very low-level number formatting to something like eformat under the egui repository, or as a its own crate in its own rerun-io repository.