server : optimize get_token_probabilities (#24796)
Use std::partial_sort to order only the requested top-n tokens instead
of the full vocabulary
logprobs sort: vocab=128000 n_top=0 iters=100
full sort: 8555.6 us/op
partial sort: 704.3 us/op
Signed-off-by: Adrien Gallouët <angt@huggingface.co>
