Unix file copy

[adrazilo]

Proposed changes

This PR fixes the unixFileCopy command on the mock server so that it properly updates the global directory and returns a message response.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

PR Checklist

• If the changes in this PR are meant for the next release / mainline, this PR targets the "staging" branch.
• My code follows the style guidelines of this project (see: Contributing guideline)
• New and existing unit tests pass locally with my changes
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works, or describe a test method below

Testing

To test this feature, please consider the following test conditions:

1. A folder/file can be copied to an from any path.
2. A folder/file does not override an existing folder/file
3. A folder/file that does not exist is not copied

Further comments

This is my first PR! It is also a great introductory task to working with the mock server.

[DivergentEuropeans]

Great job, /copy endpoint looks good to me! 🍨 Tested forceOverwrite, newName attribs too, yield proper responses

TODOs make sense