Devenv indirectly has itself as Flake input

[Cu3PO42]

Hey there! Let me start by thanking you for the work on devenv. Overall I've had a very positive experience with it so far.

However, I have noticed an explosion in Flake inputs when I added it, including many duplicates. I suddenly had six copies of nixpkgs. One of the worst offenders seem to be that one currently gets two copies of devenv by adding it once. This happens because devenv now includes cachix, which itself includes devenv, only a different version. I think adding something along the lines `cachix.inputs.devenv.follows = "self" would make a ton of sense.

More generally, I see no reason for the two not to share their version of flake-compat or pre-commit-hooks, etc.

I'd be happy to send a PR that attempts to remove some of these inputs.

[domenkozar]

Please send a PR, I'm happy to reduce that set!