fix(cmd): add network validation in coffee cmd inputs

[Anyitechs]

This PR validates the argument passed into the -n flag, and ensures only supported CLN networks are created in the /Users/User/.coffee directory, and closes #270 .

Implementation

The current implementation consists of:

• An enum (ClnNetwork) with Mainnet, Testnet, Signet, and Regtest as variants
• A ClnNetwork implementation (impl) with a from_str function that matches on the network (&str) argument and returns a ClnNetwork variant, and to_str function that matches on the ClnNetwork variant and returns the network String.
• The network function validates the -n argument.

Current Behaviour

The validation works as expected, so passing in a random name as the network name will not create the directory but the command returns the same output as below regardless of the network name. Also, passing in a random network name and running coffee -n remote list for the first time ignores the invalid network name and creates a /Users/ifeanyichukwu/.coffee/bitcoin directory for example, but running the command again doesn't create a ../.coffee/bitcoin directory again.

ifeanyichukwu@IfeanyiukwusMBP coffee % coffee -n remote list
● Plugins installed
╭───────────────────────────────────────────╮
│ ●   Language   Name   Enabled   Exec path 
├───────────────────────────────────────────┤
╰───────────────────────────────────────────╯

How to test

• cd into the coffee directory
• Run make install
• Run coffee -n remote list

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[Anyitechs]

Thank you for the review. I'll work on the requested changes and update the PR.

[Anyitechs]

Good code, some small minor changes

Thank you for the review. I've addressed all the requested changes and updated the PR.

Let me know if there's anything I'm missing.