Add Support for Amazon Bedrock Provider

Currently, the SDK includes built-in support for providers like OpenAI and Anthropic, but Bedrock — which unifies access to many high-quality foundation models — is not directly supported.
This enhancement would allow users of the SDK to leverage AWS’s scalable foundation models via a C++ interface alongside other providers.

**Motivation**
Amazon Bedrock is a fully managed AWS service that provides access to a wide range of foundation models from different providers via a single API. Bedrock supports many leading models across domains such as text, reasoning, coding, and multimodal tasks

**Proposed Solution**
Add a new provider module, e.g. ai/bedrock.h and supporting implementation similar to existing providers (openai, anthropic).
Use AWS SDK for C++ (Aws::BedrockRuntime::BedrockRuntimeClient) to handle API requests and authentication.
Expose key Bedrock features through the SDK’s unified interface (text completion, streaming, etc.).
Include examples/tests demonstrating a basic Bedrock request (e.g. text generation).

Commencez par examiner les modules de fournisseur openai et anthropic existants, puis inspectez le point d’entrée proposé ai/bedrock.h ainsi que Aws::BedrockRuntime::BedrockRuntimeClient. Définissez comment la complétion de texte, le streaming, l’authentification et l’interface unifiée doivent être mappés vers Bedrock, puis ajoutez des exemples ou des tests pour une requête élémentaire de génération de texte.

Rédigé par le modèle d'indexation à partir du texte de l'issue.