Add and Expose Type Hints

[chasleslr]

Summary

Add type hints to the codebase. This includes adding a py.typed file (as per PEP 561) to enable type checkers to use aisuite's type information effectively.

Why is this needed?

• Improves code readability and maintainability by explicitly defining function signatures and variable types.
• Enables mypy, pyright, and other type checkers to utilize aisuite's type information when users check their code.
• Provides completion suggestions for users of pylance or pyright.

Proposed Solution

1. Add Type Hints:

   • Review all functions, methods, and variables in the codebase and annotate them with appropriate type hints.

2. Add py.typed File:

   • Include a py.typed file in the package to mark it as PEP 561-compatible.

3. Integrate mypy:

   • Add mypy as a development dependency in the project.
   • Configure a mypy.ini file or equivalent to define type-checking rules.
   • Ensure mypy checks are part of the CI pipeline.

Additional Context

• Reference: PEP 484 - Type Hints
• Reference: PEP 561 - Distributing and Packaging Type Information
• Reference: mypy Documentation

[OutstandingWork]

@chasleslr I would like to work on it.