fix: Don't follow circular symlinks

[joshhunt]

Fixes the Error: ELOOP: too many symbolic links encountered exception that happens during the walkdir when the working directory contains circular symlinks.

I think this is the right logic to check this, and added some tests to try and catch the common scenarios.

[phated]

@joshhunt could we just check if the error is ELoop and bail?

[joshhunt]

@phated Could do. However, I think that's problematic because:

• I don't think we want to throw an error on circular symlinks, as some people will have these for legitimate reasons, and with no way to filter out directories from the walkdir this would just not work if you have them
• it wastes time needlessly walking through the circular symlinks
• it would emit the same file multiple times through each 'step' of the circular symlink - e.g fixtures/folderA/file-a.txt, fixtures/folderA/dest/folderA/file-a.txt, fixtures/folderA/dest/folderA/dest/folderA/file-a.txt, etc

It's up to you which you would prefer, but I'm skeptical of just waiting for ELOOP.

I think the logic in this PR is good, but I'm struggling to come up with additional test cases to better validate it...

[joshhunt]

@phated I think this is in a good spot - open for feedback, other approaches, or scenarios to test!