Add reconnection support to GatewayClient

[ncoop57]

Implements automatic reconnection handling for the Discord gateway connection with session
resumption.

Changes:

• Added method to handle connection drops and resume sessions
• Implemented heartbeat ACK tracking to detect zombie connections
• Added handling for Discord opcodes 7 (reconnect), 11 (heartbeat ACK), and 1 (heartbeat request)
• Added class method for session resumption
• Improved error handling in and methods
• Store from ready event for proper reconnection

This ensures the bot maintains its session and doesn't miss events during temporary network issues.