make sanity check when the coffe network is working in the wrong core lightning network directory

# Background

To run Coffe you are run the following command `cargo run -- --help` and you can run the following command to setup coffee for your core lightning node

```
cargo run -- setup
cargo run -- remote add lightningd https://github.com/lightningd/plugins.git
cargo run -- install
```

However, coffee should take into count also the network of core lightning, you can already do it by adding the `--netwrok testnet`, However, the current core does not make any check regarding possible network mismatch (when you are installing a conf for the testnet network on the bitcoin on)

# Goal

the following command should return an error because by default coffee is working on bitcoin network!
```
cargo run -- setup /home/vincent/.lightning/testnet/config
```

but the following command is correct

```
cargo run -- --network testnet setup /home/vincent/.lightning/testnet/config
```

Start at the CLI setup entry point exercised by `cargo run -- setup ` and trace the existing `--network` argument handling. Compare the requested network with the Core Lightning directory before setup; done means the default Bitcoin command rejects the testnet path while the explicit `--network testnet` command succeeds.

Written by the indexing model from the issue text.