* llama : add discard for deferred state writes
* llama : add tensor zeroing helper for backends without tensor memset
* llama : clear K/V data after failed sequence restore
* llama : clear recurrent state data after failed sequence restore
* llama : simplify discard and restore cleanup
* llama : report error when abnormal cell count is found in state_read_meta
* llama : clear attention state on hybrid restore failure
* tests : cover failed state restore cleanup
* llama : clear MLA state on dsa restore failure
* tests : update test for rebased test suite
* llama : clarify comment in llama_memory_recurrent::state_read