feat(tls): implement global TLS session caching for improved performance

[arman-bd]

• Added global session cache to store and retrieve TLS sessions for async requests.
• Implemented locking mechanisms for thread safety across platforms.
• Introduced functions to get and put sessions in the global cache with expiration handling.
• Enhanced client session caching with methods to store and retrieve sessions, supporting HTTP/2.
• Updated the TLS connection function to utilize cached sessions for faster reconnections.

feat(async_client): enhance AsyncClient with thread pool fallback and improved documentation

• Refactored AsyncClient to use true async I/O with a fallback to a thread pool if async bindings are unavailable.
• Improved documentation for AsyncClient and its methods, clarifying usage and functionality.
• Added support for concurrent requests using asyncio.gather.
• Updated request handling to manage headers and body more effectively.

feat(client_c): add connection pooling and pre-warming capabilities

• Introduced methods for pre-warming connections to reduce latency on subsequent requests.
• Added configuration options for connection pooling, including idle timeout and max connections.
• Implemented statistics retrieval for connection pools and cleanup of idle connections.