fix(mlx-vlm): bump mlx-vlm pin to v0.6.12 (#12818)

mlx-vlm v0.4.4 attaches the image placeholder to the last message that is
not system or assistant. After a tool call that is the tool result, which
the chat template renders as text, so the next turn fails with "Image
features and image tokens do not match: tokens: 0". v0.6.12 keeps the
placeholder on the user message that carried the image.

The v0.4.4 pin (#9568) worked around the mlx-cuda wheels stopping at
0.31.1. They are at 0.32.4 now, and v0.6.12 (mlx>=0.32.0) resolves with
mlx[cuda12] and mlx[cuda13]. v0.7.x would need backend changes: it drops
mlx_vlm.tool_parsers, which backend.py imports.

Signed-off-by: gman <genx7up@users.noreply.github.com>
Co-authored-by: Ettore Di Giacinto <mudler@users.noreply.github.com>

backend/python/mlx-vlm/requirements-cpu.txt

@@ -1,2 +1,2 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 mlx[cpu]

backend/python/mlx-vlm/requirements-cublas12.txt

@@ -1,2 +1,2 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 mlx[cuda12]

backend/python/mlx-vlm/requirements-cublas13.txt

@@ -1,2 +1,2 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 mlx[cuda13]

backend/python/mlx-vlm/requirements-l4t12.txt

@@ -1,2 +1,2 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 mlx[cuda12]

backend/python/mlx-vlm/requirements-l4t13.txt

@@ -1,2 +1,2 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 mlx[cuda13]

backend/python/mlx-vlm/requirements-mps.txt

@@ -1,3 +1,3 @@
-git+https://github.com/Blaizzy/mlx-vlm@v0.4.4
+git+https://github.com/Blaizzy/mlx-vlm@v0.6.12
 torch
 torchvision