Ft_lstdelone extra tests proposal

[Anloms]

Hi! My name is Ola, and I’m a new cadet from 42 London. While completing libft and using your testing framework (which is an absolute gift — thank you!), I noticed that the ft_lstdelone tests could benefit from a couple of additional cases:

• Testing the first parameter: calling the function with NULL as the list node.
• Testing the second parameter: using a dummy delete function to ensure behavior is consistent.
• Testing deletion of a middle node: verifying that deleting one node does not affect the content of the next node.

I’ve implemented these improvements in my fork and would love to propose them via a pull request.
Please let me know if this aligns with your vision for the project — I’m happy to adjust anything if needed.

Best,
Ola