feat: allow overrides of inputs of projects that don't use flake.lock

[jbgi]

as well as following their inputs.
This override feature for dependencies with empty flake inputs is only effective when a dependency use the following (or functionally similar) pattern:

#default.nix
{
  inputsOverrides ? { },
}:
let
  withInputs = import ./with-inputs.nix [ ./follows.nix inputsOverrides ];
in
withInputs ./outputs.nix

and

#flake.nix
{ outputs = inputs: import ./. { inputsOverrides = removeAttrs inputs [ "self" ]; }; }

This patch also add the additional capability of following/accessing inputs of dependencies that does not use flake inputs put still provides a non empty inputs in their outputs (such as projects using with-inputs).

[vic]

Code looks good, can you please fix the CI error by running that command locally ?