Fix duplicate member entries in Scaladoc generation

[cheeseng]

Resolves an issue where Scaladoc was generating duplicate entries for the same members when combining results from multiple parser instances.

The fix implements deduplication by creating a stable composite key from the member's location, full name, and kind. When duplicates are found, the entry with documentation is preferred, falling back to the first entry if none have docs.

This ensures clean, non-redundant API documentation output.