This changes our logic for detecting duplicate definitions on case-sensitive file-systems to only operate on files of interest and to fix this detection logic per issue OpenCyphal#104.

If globular searches find duplicates we do not waste time detecting this until/unless these duplicates are actually considered when parsing target definitions.

Promoting case-sensitivity issue from assertion error to DataTypeNameCollisionError

Co-authored-by: Pavel Kirienko <[email protected]>