Fix AttributeError: 'Project' object has no attribute 'datafile_controller'

[chelslava]

Summary

• Fixes crash when using Library Finder on a clean install without an open project
• Adds datafile_controller property to Project class
• Adds null checks in _ImportSuggester to handle when datafile_controller is None

Problem

When RIDE is started fresh (clean install) without an open project, calling Tools -> Library Finder... crashes with:

AttributeError: 'Project' object has no attribute 'datafile_controller'

Root Cause

_ImportSuggester.__init__() calls controller.datafile_controller, but Project class didn't have this property. The datafile_controller attribute only existed on _DataController subclasses.

Solution

1. Added datafile_controller property to Project class that returns self.controller (which may be None)
2. Added null checks in _ImportSuggester.get_suggestions() and get_already_imported() to gracefully handle the case when no project is open

Testing

• Manually tested the scenario described in the issue
• Library Finder dialog now opens without crashing on a clean install

Closes #2989