feat: add isolated GPTQ-to-OpenVINO export environment under envs/openvino

[k-arima-3150]

Summary

This PR adds an isolated OpenVINO 2026.3.1 export environment under
envs/openvino/. It provides a repeatable workflow for converting OneComp
GPTQ 4-bit checkpoints to OpenVINO IR and running inference with OpenVINO
GenAI on NPU.

• Isolated environment (envs/openvino/pyproject.toml and
  envs/openvino/uv.lock): provides pinned conversion dependencies in a
  dedicated .venv, independently of the main OneComp environment. It uses
  OpenVINO 2026.3.1 with the matching OpenVINO GenAI and OpenVINO Tokenizers
  2026.3.1.0 releases.
• Export example (envs/openvino/example_export_openvino.py): exports
  supported text-generation checkpoints while preserving their existing GPTQ
  4-bit weights. It also saves the Hugging Face tokenizer files and the
  OpenVINO tokenizer and detokenizer IR required by OpenVINO GenAI.
• Compatibility utilities (envs/openvino/openvino_export_utils.py):
  when modules_in_block_to_quantize uses the legacy flat List[str] shape,
  the exporter copies the checkpoint to a temporary directory and normalizes
  the copied configuration to List[List[str]] before Transformers and
  Optimum Intel load it. The source checkpoint is not modified.
• Documentation (envs/openvino/README.md): describes environment setup,
  checkpoint preparation, configuration of MODEL_PATH and OUT_DIR, export
  execution, NPU inference, and the changes required when adapting the example
  to a VLM.

Notes

• This environment is intentionally isolated and does not modify the
  repository-root pyproject.toml or uv.lock.
• Legacy flat checkpoint metadata requires a temporary copy of the checkpoint.
  TMPDIR can be set to an existing directory on a filesystem with sufficient
  capacity when the default temporary directory is too small.

Validation

• uv lock --check --project envs/openvino
• uv pip check --python envs/openvino/.venv/bin/python
• Import of openvino_genai
• OpenVINO tokenizer and detokenizer conversion
• Full export and IR parsing with an actual OneComp GPTQ 4-bit checkpoint
• OpenVINO GenAI inference on NPU using the exported IR

Changes

Environment

• Add an isolated OpenVINO 2026.3.1 environment with locked conversion dependencies and a
  OneComp GPTQ 4-bit export example for text-generation models. Flat checkpoint
  metadata is normalized in a temporary copy without modifying the source checkpoint.

[aki916f]

LGTM