chore(deps): bump transformers to 5.12.1 for MiniMax H3

[Rockdu]

What

• Bump transformers from 5.5.4 to 5.12.1.

Why

MiniMax H3's text encoder (Qwen3-VL) imports transformers.vision_utils, which does not exist in 5.5.4. The current H3 document requires extra environment setup, so here we bump transformers and run end-to-end CI.

Validation

uv pip install --dry-run -r requirements.txt against the CI image (transformers 5.5.4, huggingface-hub 1.15.0, torch 2.11.0+cu129):

Resolved 207 packages
 - transformers==5.5.4
 + transformers==5.12.1

Only transformers changes; no other pin is disturbed and nothing else is downgraded. (cryptography / distro / pyparsing also appear as installs, but they show up identically on an unmodified requirements.txt — pre-existing gaps in the image, not caused by this bump.)

Files

File	Role
requirements.txt	the bump, plus a comment recording the vision_utils floor and why 5.12.1

Checklist

• pre-commit run --all-files passes — not run locally
• Added/updated tests for new behaviour — none added; a version bump has no behaviour of its own, CI is the test
• pytest -x is green — not run locally (no torch in this environment); relying on CI
• If launch flags changed, python3 train.py --help still parses — no flags changed
• If a public flag was added, it appears in the CLI reference docs — no flags added
• If an example was added, it has a real walkthrough — no examples added