llama : refactor sampling_info to use buffer_view template (ggml-org#19368)

* llama : refactor sampling_info to use buffer_view template

This commit updates the sampling_info struct in llama-context to use a
buffer_view template for the logits, probs, sampled tokens, and
candidates buffers.

The motivation for this is to simplify the code, improve type safety
and readability.

Author: danbev