chore(deps): bump mlx-lm to >=0.31.1 so Qwen3.5 architecture is supported (#282)

uv.lock pinned mlx-lm==0.29.1, which predates the qwen3_5 architecture.
Running mlx_lm.server with mlx-community/Qwen3.5-* models therefore
fails with 'Model type qwen3_5 not supported.' on every uv sync, even
when pyproject.toml's loose constraint (>=0.19) would otherwise allow
a newer release.

Tighten the inference-mlx extra to mlx-lm>=0.31.1 (the first release
with Qwen3.5 support) and regenerate uv.lock — resolves to mlx-lm
0.31.3.

The lockfile diff is large because uv produces a single cross-platform
lock and adds 'split' entries for a handful of transitive deps
(transformers, vllm, huggingface-hub, mistral-common, etc.). Every
split entry is marker-gated to:

    python_full_version >= '3.14' and sys_platform != 'linux'
    and sys_platform != 'win32'

i.e. macOS on Python 3.14+ — the very subset that actually pulls in
mlx-lm 0.31.x. Linux, Windows, and Python <= 3.13 paths keep the
existing pins (transformers 4.57.6, vllm 0.17.1, …).

Closes #191

pyproject.toml

@@ -45,7 +45,7 @@ dev = [
     "ruff>=0.4",
     "pre-commit>=3.0",
 ]
-inference-mlx = ["mlx-lm>=0.19; sys_platform == 'darwin'"]
+inference-mlx = ["mlx-lm>=0.31.1; sys_platform == 'darwin'"]
 inference-vllm = ["vllm>=0.16.0"]
 inference-cloud = [
     "openai>=1.30",