`maint/downgrad_dependencies` - switch to --direct-minimal-versions

The maint/downgrad_dependencies script currently uses --minimal-versions, which is not recommended for this usecase (or really, for any usecase).

We should switch to --direct-minimal-versions. However, this seems to detect conflicts in a sort of strange way across the entire workspace. We can either harmonize our versions across the entire workspace (probably worth doing anyways?), or wait until something like https://github.com/taiki-e/cargo-minimal-versions/issues/1 is available.