Enhanced file resolution in analyzer.py

Updated resolve_local_import() to check nested subdirectories (up to 2 levels deep) when searching for local files
Finds files in paths like src/data/spreadsheet_creation/spreadsheet_formatting_dataclasses.py
Checks all subdirectories of parent directories, not just common ones like _shared
Stricter dependency extraction in manager.py:
Only adds ambiguous imports as dependencies if they can be verified as installed packages
If an import can't be verified as a package, it's skipped (likely a local file that wasn't resolved)
Prevents adding local files as third-party dependencies
Added tests:
Created tests/test_spreadsheet_creation_imports.py to verify files in nested subdirectories are correctly identified as external dependencies and copied, not added as third-party packages

Full Changelog: v2.0.6...v2.0.7