- Fix file handle usage with Path.open() instead of open()
- Add type annotations to test methods and fixtures
- Comment out unused test variables
- Add type annotation for empty list initialization
- Fix unused mock_monorepo argument

- Remove commented-out code (ERA001) from test_pip_indices.py and test_pip_indices_integration.py
- Add missing pip_indices argument to create_conda_env_specification calls
- Fix type annotations: use list[str] instead of list[Platform] with type ignores where needed
- Add __future__ annotations import and update typing imports
- Fix unused arguments with noqa comments
- Consolidate nested with statements
- Mark hardcoded test password with noqa comment
- Clean up indentation issues

All pre-commit hooks now pass: ruff, ruff-format, and mypy

- Add pip_indices to the list of supported configuration keys
- Include examples in both requirements.yaml and pyproject.toml formats
- Create dedicated "Custom Pip Index URLs" section with:
  - Clear explanation of use cases (private packages, mirrors, authenticated repos)
  - How it works (primary vs extra indices, env var expansion, deduplication)
  - Practical examples for common scenarios (GitLab, Artifactory, PyTorch)
  - Generated environment.yaml output format
  - Security best practices for credentials
- Update table of contents to include new section
- Reference Conda CEP-8 specification for pip_repositories field

The documentation provides clear guidance for users needing to access
private or alternative package repositories while maintaining security
best practices.

- Change _pip_install to _pip_install_local (the actual function name)
- Change generate_conda_lock to conda_lock_command (the actual function name)

This fixes the CI test failures caused by attempting to mock non-existent functions.

- Changed back from list[str] to list[Platform]
- Removed unnecessary # type: ignore[arg-type] comments
- Added proper import of Platform from unidep.platform_definitions

This corrects a mistake where I incorrectly changed the type annotations
to work around an import issue instead of fixing the import properly.

The pip_repositories field is not part of any official Conda Enhancement Proposal (CEP).
CEP-8 (PR #8 in conda/ceps) is actually about menuinst multiplatform support, not pip repositories.

The pip_repositories field appears to be an unofficial extension that may be used
by conda-lock or other tools, but it's not a formal specification.