feat: add AfricasTalking SMS adapter

[deepshekhardas]

Summary

Adds a new SMS adapter for AfricasTalking API.

Changes

• New Adapter: Utopia\Messaging\Adapter\SMS\AfricasTalking
• Supports sending SMS messages with optional sender ID
• Handles up to 100 messages per request
• Proper error handling with API error message extraction

Usage

use Utopia\Messaging\Adapter\SMS\AfricasTalking;
use Utopia\Messaging\Messages\SMS;

$sender = new AfricasTalking('username', 'api_key');

$message = new SMS(
    to: ['+254700000000'],
    content: 'Hello World',
    from: 'MY_SENDER_ID' // optional
);

$response = $sender->send($message);

Test Plan

• Integration tests with environment-gated credentials
• Tests both with and without custom sender ID

---

Summary by cubic

Adds an AfricasTalking SMS adapter and a new Messenger failover utility, plus new SMS adapters for Alibaba Cloud and Vonage. Also improves Mailgun and Msg91 handling for better compatibility and error reporting.

• New Features

  • AfricasTalking SMS adapter: optional sender, up to 100 recipients per request, clear error extraction.
  • Alibaba Cloud SMS adapter: signed GET requests with query-string signature.
  • Vonage adapters: new VonageMessages (v1 API) and VonageLegacy (classic REST).
  • Messenger class: send via multiple adapters with automatic failover, type validation, and per-request limits.

• Bug Fixes

  • Mailgun: support named recipients in "to", fix Reply-To header, and correct From formatting.
  • Msg91: extract API error messages instead of generic errors.
  • Vonage: guard against empty recipients and unify error handling.

^{Written for commit 075c715. Summary will update on new commits.}