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).

Inizia esaminando i moduli provider openai e anthropic esistenti, quindi ispeziona l’entry point proposto ai/bedrock.h e Aws::BedrockRuntime::BedrockRuntimeClient. Definisci come mappare su Bedrock il completamento del testo, lo streaming, l’autenticazione e l’interfaccia unificata, quindi aggiungi esempi o test per una richiesta di base di generazione del testo.

Scritto dal modello di indicizzazione a partire dal testo della issue.