ci dep recorder: unify dedup logic, deduplicate collection entries too
Use a single dedup_key for all phases:
- execution phase: test file path
- collection phase (opt-in): '__collection__' special key
Removes the separate dedup block, simplifies _record_import_chain.
Collection entries now deduplicated when CI_RECORD_DEPS_INCLUDE_COLLECTION=1
(771 unique vs 6823+ repeated for clip modeling test).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>