llama : fix llama_copy_state_data with fragmented KV cache (#5840)

llama : fix llama_copy_state_data with fragmented KV cache (#5840)

The row size of the saved states was based on kv_self.head while
it should be based on llama_kv_cache_cell_max.

Existing session files should still work.

* llama : fix llama_kv_cache_cell_max inability to return 1

I've also changed its return type to uint32_t,
because this function is always used to set the value of uint32_t variables,
and because the index already has this type.

* llama : fix state size calculation

Some bytes in the state were unaccounted for in llama_get_state_size.
Since the logits reserve so much space, it did not cause problems.