chore: bump mlx-swift-lm to pick up the GlmOcr and Qwen25VL unit tests (#150)

Points at 512dcde, which carries both:

- SharpAI/mlx-swift-lm#53 — MLXVLM/Models/GlmOcr.swift, whose base config
  overlays the same top-level container as text_config/vision_config
- SharpAI/mlx-swift-lm#54 — MLXVLM/Models/Qwen25VL.swift, whose text config
  does the same, with several fields duplicated across two parallel structs

Both were, alongside Gemma4/Qwen3VL/Qwen35/LFM2VL (#147-#149), among the
largest zero-coverage files in the model layer. Coverage: GlmOcr 0% → 37.9%,
Qwen25VL 0% → 26.7%.

No SwiftLM-side code changes; verified the umbrella builds clean against the
bumped pointer.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: solderzzc