Anthropic supports passing flags for beta features via beta headers in requests to its API. This PR allows for passing in the desired beta features via the $options parameter in the invoke function like so:

$platform->invoke($model, $messageBag, [
            'temperature' => 1.0,
            'max_tokens' => 20000,
            // can now include beta features like this:
            'beta_features' => [
                'code-execution-2025-05-22',
                'mcp-client-2025-04-04'
            ]
        ]);

If the beta features option is set and contains at least one element, the beta header is constructed inside the model client and then the option is removed from $options before the request is built and sent to Anthropic.

If we want to support beta feature flags for other providers in the future, we should perhaps add another parameter to the invoke function for platforms and the request function for model clients in order to not pollute $options (after all, $options is meant to hold model options not platform options).