Idea: `cargo crev expand <crate> [<version>]`

We could `cargo-expand` for allowing reviewing the crate code conveniently without having to `cd` to a given directory.

We should probably expand `build.rs` and any other file like this too.

Start by reviewing the existing cargo-crev CLI entry points and comparing the requested `cargo crev expand []` behavior with `cargo-expand`. Determine how the command should locate a crate and whether `build.rs` and other files are included; done means the requested command supports the stated arguments and expands the relevant crate code without requiring a directory change.

Written by the indexing model from the issue text.