feat(python): add mypy_exclude config option

[jsklan]

Description

Refs: Customer request for Square API SDK generation

Adds a new mypy_exclude custom config option to the Python SDK generator.

Link to Devin run: https://app.devin.ai/sessions/30e24064a098405eb1a1a2949e4a95c0
Requested by: @jsklan

Changes Made

• Add mypy_exclude custom config option that generates exclude = [...] in the [tool.mypy] section of pyproject.toml
• This is useful when .fernignore preserves directories (like legacy/ or tests/integration/) that contain code incompatible with the generated SDK
• Add python-mypy-exclude test fixture with two variants demonstrating the feature
• Bump version to 4.49.0 (minor version bump required for feat change type)

Example usage in generators.yml:

config:
  mypy_exclude:
    - "legacy/"
    - "tests/integration/"

Generated output in pyproject.toml:

[tool.mypy]
plugins = ["pydantic.mypy"]
exclude = ["legacy/", "tests/integration/"]

Testing

• Added python-mypy-exclude fixture with no-custom-config and with-mypy-exclude variants
• Seed tests pass for both variants
• Pre-commit hooks pass

Human Review Checklist

• Verify the exclude patterns are correctly formatted in the generated pyproject.toml
• Confirm the config flows correctly through abstract_generator.py → project.py → pyproject_toml.py

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring