Update "Rust - Cargo" example - #1799

This PR brings the "Rust - Cargo" example inline with the Cargo book.

Supersedes #1167.

Description

This PR adds entries for files .crates.toml and .crates2.json to the existing four directories:

* `.crates.toml`
* `.crates2.json`
* `bin/`
* `registry/index/`
* `registry/cache/`
* `git/db/`

Motivation and Context

Not having those files cached can cause spurious errors. For example, suppose one has cargo-expand@1.0.125 installed and one tries to install cargo-expand@1.0.126 with the command cargo install cargo-expand. With the files cached, the installation completes successfully. Without it, one could see an error like this:

error: binary `cargo-expand` already exists in destination

How Has This Been Tested?

Here are two workflows demonstrating the above claims:

• Without .crates.toml and .crates2.json (cargo install cargo-expand fails)
• With .crates.toml and .crates2.json (cargo install cargo-expand succeeds)

For reference, here is a comparison of the two branches on which the workflows were run: smoelius/cache-experiment@main...with-crates-toml-crates2-json

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (add or update README or docs)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.