UPSTREAM PR #18789: server: improve slots scheduling for n_cmpl

[loci-dev]

Mirrored from ggml-org/llama.cpp#18789

Ref: ggml-org/llama.cpp#18663 (comment)

This PR introduces scheduling mechanism inspired by thread barrier, which allow launching n_cmpl slots at the same time.

I tested with repeated requests to /v1/completions using the following payload:

{
    "prompt": "I believe the meaning of life is",
    "stream": false,
    "n": 3,
    "n_predict": 100,
    "id_slot": 0
}

And so far it works correctly

[loci-review]

Explore the complete analysis inside the Version Insights

Based on the analysis, no functions were identified with meaningful performance changes between the base and target versions. The code modifications did not result in measurable performance impact.

[loci-review]

Explore the complete analysis inside the Version Insights

Based on the analysis, no functions were identified with meaningful performance changes between the base and target versions. The code modifications did not result in measurable performance impact.