✨ Feat: add ability to use example files

[bucsi]

My puzzle workflow is usually the following:

1. understand the task
2. write a solution
3. run the solution with the example input in the task
4. debug the solution
5. run the solution for my puzzle input
6. write solution for the 2nd part
7. repeat 3-5.

With gladvent, steps 5 and 7 always involve deleting my puzzle input from the input file, then copying it back.

With this PR:

• the new command creates a {day}.example.txt file as well
• I introduced a new bool flag for the run command, --use-example. If it is present, the runner will pass the example txt as input

If I missed anything, please reach out and I'll gladly update my PR.

[TanklesXL]

Thanks for the contribution! I haven't looked at the code yet but upon reading the description I wonder if it's worth putting the example generation behind a flag.

I would probably replace the --use-example group flag from the run group with a group flag of --example at the root so it can be used for both generation via new and running via run and run all.

[TanklesXL]

Thanks a bunch! merged