Rollup merge of rust-lang#127923 - ferrocene:use-reuse-tool-4.0, r=pietroalbini

Use reuse tool 4.0

This change upgrades us to reuse-tool 4.0.3, which has a new TOML format configuration instead of the old `.reuse/dep5` Debian-style file.

* Updated requirements file to install reuse-4.0.3
* Ran `reuse convert-dep5` to switch to new file format
* Switched over to `override` so the `REUSE.toml` file takes precedence over whatever random Copyright strings `reuse` finds in the source tree.

Should fix rust-lang#127361

Author: tgross35