context : allow cache-less context for embeddings (#13108)

context : allow cache-less context for embeddings (#13108)

* context : allow cache-less context for embeddings

ggml-ci

* context : enable reranking with encode()

ggml-ci

* context : encode() clears embd_seq

ggml-ci

* examples : use llama_encode() when appropriate

ggml-ci

* models : nomic bert moe does not require KV cache

* llama : update comments for llama_decode/llama_encode

ggml-ci

* context : update warning log [no ci]