Initial commit: OpenRouter Python SDK

Auto-generated Python SDK for OpenRouter API, providing comprehensive client library with:
- Chat completions and streaming support
- Embeddings API
- Model and provider information
- API key management
- Analytics and usage tracking
- OAuth authentication flows
- Full type hints and error handling

CONTRIBUTING.md

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+# Contributing to This Repository
+
+Thank you for your interest in contributing to this repository. Please note that this repository contains generated code. As such, we do not accept direct changes or pull requests. Instead, we encourage you to follow the guidelines below to report issues and suggest improvements.
+
+## How to Report Issues
+
+If you encounter any bugs or have suggestions for improvements, please open an issue on GitHub. When reporting an issue, please provide as much detail as possible to help us reproduce the problem. This includes:
+
+- A clear and descriptive title
+- Steps to reproduce the issue
+- Expected and actual behavior
+- Any relevant logs, screenshots, or error messages
+- Information about your environment (e.g., operating system, software versions)
+    - For example can be collected using the `npx envinfo` command from your terminal if you have Node.js installed
+
+## Issue Triage and Upstream Fixes
+
+We will review and triage issues as quickly as possible. Our goal is to address bugs and incorporate improvements in the upstream source code. Fixes will be included in the next generation of the generated code.
+
+## Contact
+
+If you have any questions or need further assistance, please feel free to reach out by opening an issue.
+
+Thank you for your understanding and cooperation!
+
+The Maintainers