feat: validate if config is a DAG

[legosandorigami]

@scriptnull

This PR addresses issue #15 by implementing and providing the following four test cases:

1. Valid DAG
   

2. Valid DAG
   

3. Invalid DAG
   

4. Invalid DAG
   

To maintain the encapsulation of the Connector struct, I kept the fields unexported. However, I introduced the following two methods to the Connector interface:

From() string

To() string

I have successfully run the tests locally and confirmed that everything is working as expected. Please feel free to review and suggest any improvements or changes. I apologize in advance for any oversights.

[scriptnull]

Hi, Thanks for the pull request! I will get back to you once I find some free time to review it!

[legosandorigami]

@scriptnull,

I wanted to acknowledge and apologize for an oversight in the cycle detection algorithm I contributed. I initially used code from ChatGPT without fully verifying it. While the rest of the work in the PR was original, I realize this was a lapse in my process.

I have corrected the algorithm and tested it to ensure its accuracy. My data structures and algorithms skills were a bit rusty, which contributed to this oversight. I am committed to improving and ensure that this does not happen again.

Thank you for your understanding and for reviewing my PR.