feat: migrate to PEP 420 namespace package structure

[vishalg0wda]

Summary

Migrates the SDK to use PEP 420 implicit namespace packages, enabling future mistralai.workflows subpackage to be managed separately.

Breaking Change: Import paths change from from mistralai import X to from mistralai.sdk import X

Changes

• Configure moduleName: mistralai.sdk in gen.yaml for namespace package support
• Generate SDK with new namespace structure (src/mistralai/sdk/)
• Migrate custom code regions to new SDK location
• Update import paths in extra/ package
• Fix py.typed marker paths in pyproject.toml
• Restore custom hooks (custom_user_agent, deprecation_warning, tracing)
• Configure mypy for PEP 420 namespace packages

New Structure

src/mistralai/           # PEP 420 namespace (no __init__.py)
├── sdk/                 # Generated SDK
├── extra/               # Custom extensions
└── (future: workflows/) # Separately managed package

Test Plan

• All existing tests pass
• Package builds successfully (uv build)
• Import paths verified working
• pylint passes (10.00/10)
• mypy passes (no issues in 304 source files)
• Published to test PyPI and verified installation

Test PyPI Verification

Published and tested at: https://test.pypi.org/project/mistralai/1.11.0/

# Install from test PyPI
uv pip install --index-strategy unsafe-best-match \
  --index-url https://test.pypi.org/simple/ \
  --extra-index-url https://pypi.org/simple/ \
  mistralai==1.11.0

# Verified imports work correctly
python -c "from mistralai.sdk import Mistral; print(Mistral)"
# <class 'mistralai.sdk.sdk.Mistral'>

python -c "from mistralai.sdk.models import ChatCompletionRequest; print(ChatCompletionRequest)"
# <class 'mistralai.sdk.models.chatcompletionrequest.ChatCompletionRequest'>

Migration Guide

# Before (v1.x)
from mistralai import Mistral
from mistralai.models import ChatCompletionRequest

# After (v2.x)
from mistralai.sdk import Mistral
from mistralai.sdk.models import ChatCompletionRequest