Fix bulk edit validation: prevent duplicate findings from being active/verified (#13965)

* Fix bulk edit validation: prevent duplicate findings from being active/verified

- Add validation in FindingBulkUpdateForm to prevent active findings from being risk accepted
- Add view-level validation to check existing duplicate status before setting active/verified
- Add view-level validation to check existing active status before risk accepting
- Add comprehensive user feedback for skipped findings with reasons
- Track actually_updated_count to accurately report successful updates

Fixes #11336

* add bulk edit validation tests

* bulk edit: reduce method complexity

Author: valentijnscholten