Fix Mypy Static Type Checking Errors in Export Modules

[omen18]

Bug Report: Mypy Static Type Checking Errors in Export Modules

Description

When running mypy python/src on the coreai-models Python package, several static type checking errors occur due to variable scoping/shadowing and type annotations in model export modules:

1. Union type ambiguity in segmentation/export.py:
   The config variable is assigned a FullExportConfig instance in the if args.full: branch and a SegmentationExportConfig instance in the else: branch. Consequently, static type checkers evaluate config as a union (FullExportConfig | SegmentationExportConfig), causing type errors when accessing fields unique to SegmentationExportConfig (such as max_text_seq_len, image_n_bits, image_group_size, text_n_bits, text_group_size).

2. ExportConfig variant literal assignment in llm/export.py:
   The variant string parsed from command-line arguments is passed to ExportConfig(...), which expects Literal['macOS', 'iOS'], causing an arg-type mismatch.

3. Variable name shadowing in vlm/export.py:
   The spec variable used in the --list-models iteration loop (for name, spec in SUPPORTED_MODELS.items():) shadows the lookup result of spec = SUPPORTED_MODELS.get(args.model) later in main().

Steps to Reproduce

1. In the repository root, install dependencies with uv sync.
2. Run uv run mypy python/src.
3. Observe the reported type errors.

Expected Behavior

mypy python/src should evaluate exported CLI tools and pipeline modules with zero static type errors.

Suggested Fix

• Disambiguate config -> seg_config in segmentation/export.py.
• Explicitly cast/narrow variant to Literal["macOS", "iOS"] in llm/export.py.
• Rename loop variable in vlm/export.py from spec to target_spec.