Ensure all working directory changes are Paths

The `Tool.run()` method has the following signature:

```py
def run(self,
additional_parameters: Optional[
Union[str, Sequence[Union[Path, str]]]] = None,
profile: Optional[str] = None,
env: Optional[Dict[str, str]] = None,
cwd: Optional[Union[Path, str]] = None,
capture_output=True) -> str:
```

It would be cleaner if the caller was required to ensure `cwd` was a `Path` instance. This would also allow the `FabCommandError` exception constructor to be cleaned up.

Start by locating Tool.run() and the FabCommandError constructor, then inspect their callers to see how cwd is currently supplied. Update the working-directory interfaces so callers use Path values and confirm that FabCommandError no longer needs its existing path-handling cleanup.

Written by the indexing model from the issue text.