Fix build in docker (for rust)

[DrEverr]

Rust cargo build should not rebuild when there where no changes made.

[DrEverr]

What if we introduced a service cache that generates a cache.json file, for example:

{
  "services": [
    {
      "name": "example",
      "hash": "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
    }
  ]
}

If the service code changes (and therefore its hash changes), we would only rebuild that specific service.

The hash should be computed from all files (ideally, we should respect .gitignore if it exists) in the service directory.

It’s better for the hash to include more files rather than fewer, to avoid missing meaningful changes.