feat: add Albert API support

[OskarStark]

Description

This PR adds support for Albert API, the French government's sovereign AI gateway. Albert provides an OpenAI-compatible API interface for various language models while ensuring data sovereignty and compliance with French/EU regulations.

Key Features

• 🇫🇷 Sovereign AI: Albert is hosted and operated by the French government
• 🔧 OpenAI-compatible: Uses the same API structure as OpenAI
• 🔒 Data Privacy: Ensures data remains within French/EU jurisdiction
• 🎯 Public Sector Focus: Designed for use by French public administration

Implementation Details

• Created Albert-specific model clients (GPTModelClient and EmbeddingsModelClient) with configurable base URL
• Added PlatformFactory for easy Albert API initialization
• Reuses OpenAI's response converters for compatibility
• Supports both chat completions and embeddings endpoints

Usage Example

use PhpLlm\LlmChain\Platform\Bridge\Albert\PlatformFactory;
use PhpLlm\LlmChain\Platform\Bridge\OpenAI\GPT;

$platform = PlatformFactory::create(
    apiKey: $_ENV['ALBERT_API_KEY'],
    albertUrl: $_ENV['ALBERT_API_URL']
);

$model = new GPT('gpt-4o');
$chain = new Chain($platform, $model);

Testing

• Added unit tests for PlatformFactory
• Added example script demonstrating Albert API usage with RAG context
• All tests pass and code follows project standards

Documentation

• Updated README to list Albert as a supported platform
• Added example file showing how to use Albert API
• Included context about French AI strategy in the example

This implementation allows French public sector organizations to leverage LLM Chain while maintaining data sovereignty and regulatory compliance.