iOS: Update TwilioConversationsClient to 4.0.3+

[martintrollip]

Description

This issue tracks the implementation of TwilioConversationsClient version 4.0.3 or higher. The challenge arises from Twilio's shift away from CocoaPods in favor of Swift Package Manager (SPM).

Current State

• CocoaPods is used for iOS dependencies
• TwilioConversationsClient version 4.0.3+ is only available through SPM and not on CocoaPods

Technical Requirements

1. Maintain existing CocoaPods integration for Flutter compatibility
2. Add SPM support specifically for TwilioConversationsClient
3. Ensure both dependency managers coexist without conflicts

Implementation Approach

1. Enable SPM in Flutter environment:

flutter config --enable-swift-package-manager

2. Add Twilio dependency via SPM:

// Package.swift
dependencies: [
    .package(url: "https://github.com/twilio/conversations-ios", from: "4.0.3")
]

3. Maintain CocoaPods configuration for other dependencies
4. Determine if this is a breaking change

Related Documentation

• Twilio's official stance on package managers
• Flutter's SPM integration guide