Modernizes the Dart extractor: comment stripping, `part of` redirection, nested-generic-aware extends/with/implements parsing, generic type-argument mapping, and generic call detection.
Verified against current v8: merges cleanly, full suite 1530 passed, and inheritance edges connect to same-file class nodes with no ghost-node splits or dangling edges (consistent with the #1033/#1096 node-ID invariants).
Alexey Z