[attention backends] fix ring CP for flash and flash 3 (#13182)
* tests: add cp backend and attention backend tests.
* up
* up
* up
* fix ring for flash and flash_3
* generate.
* Apply suggestions from code review
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>
* up
* up
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Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>