simple format command for running all of the formatters

[delicious-lemon]

We have numerous format commands in the Makefile. Let's add a flake app workflow that lets us format everything at once.

[srid]

a flake app workflow

@MatthewCroughan and/or I would like to simplify the overengineered branch one day, but for now you could use lint-utils:

• flake input: https://github.com/srid/haskell-template/blob/41229a73eda937072b322ceda4d1d6fd7352067c/flake.nix#L11-L16
• spec: https://github.com/srid/haskell-template/blob/41229a73eda937072b322ceda4d1d6fd7352067c/flake.nix#L68-L75
• nix run: https://github.com/srid/haskell-template/blob/41229a73eda937072b322ceda4d1d6fd7352067c/flake.nix#L88
• as check: https://github.com/ArdanaLabs/dUSD/blob/eaf9da9f7fc47f530e5482b551dde0e1f5ebcc14/flake.nix#L252

[srid]

This is probably better: https://github.com/numtide/treefmt

Demo: https://github.com/srid/emanote/pull/283