Update base for Update on "[Executorch][llm] Add support for ring kv cache and ring attention"

Introduced CachePositionManager to keep track of what is the position for each slot in ring kv cache. This is used to generate mask.

Differential Revision: [D73891427](https://our.internmc.facebook.com/intern/diff/D73891427/)

[ghstack-poisoned]

Author: kimishpatel