prepare seems to bring some unnecessary files when used with --bin

[0xangelo]

Hi, I've been noticing some cache misses when building out containerized bins in a Cargo workspace, so I set up https://github.com/0xangelo/cargo-workspace-template to experiment with.

In there you'll see two crates with binary targets: hello-world and goodbye-world. The former has a binary with the same name. The latter has 2 bins and importantly, no dependencies.

Here's my experiments with cargo chef prepare --bin with each of the 3 binaries

The difference between the recipes for hello-world and goodbye-world are as expected: the root Cargo.toml generated only includes the respective crates defining those binaries.

However, you'll notice above that for hasta-la-vista (the other binary of the goodbye-world crate), it includes all the crates in the workspace. Seems unnecessary as it has no dependencies on any other crates in the project.

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On a general note: would it be possible to enhance prepare --bin in a way that the .skeleton.lock_file in recipe.json only includes the contents necessary to build the --bin in question? For instance, for the goodbye-world bin in the example repo above, that would mean the Cargo.lock contents in recipe.json would just be

# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
version = 4

[[package]]
name = "goodbye-world"
version = "0.0.1"

So, if one made changes to, say, hello-world dependencies only, that would not change the 'recipe' for goodbye-world, so we could keep the dependencies cached for that binary (well, not a great example since that binary doesn't have deps, but imagine it had one). I'd be willing to work on such feature