Add Null Safety on Connect/Disconnect Pusher

[YussufEssam89]

Pull Request: Add Null Safety to Pusher Connect/Disconnect Methods

Summary

This PR enhances the stability of the Pusher Channels Flutter plugin by adding null safety to the connect and disconnect methods. It ensures the pusher instance is safely accessed, preventing potential runtime crashes.

Changes Made

• Applied optional chaining to pusher in the following methods:
  • connect(result:)

    // Updated from:
    pusher.connect()
    
    // To:
    pusher?.connect()

  • disconnect(result:)

    // Updated from:
    pusher.disconnect()
    
    // To:
    pusher?.disconnect()

Motivation

Previously, calling connect() or disconnect() without initializing the pusher instance could result in a crash. Adding null safety:

• Prevents unsafe access to pusher
• Improves plugin reliability
• Aligns with Swift best practices for handling optionals

Testing

• Verified that calling connect() and disconnect() before initialization no longer causes crashes.
• Manually tested plugin behavior under various initialization states to confirm expected outcomes.

Notes

• No changes were made to existing logic or external plugin behavior.
• This update is fully backward-compatible.