fix(file_finder): prevent traversal attacks

[ryancragun]

How to read this pull request

Protect against traversal attacks when walking directories for enos files

Checklist

• The commit message includes an explanation of the changes
• Manual validation of the changes have been performed (if possible)
• New or modified code has requisite test coverage (if possible)
• I have performed a self-review of the changes
• I have made necessary changes and/or pull requests for documentation
• I have written useful comments in the code