Code Execution Beta Header Latest Version is Not Supported

The latest beta header for the code execution tool is `code-execution-2025-08-25` yet in [AnthropicBeta](https://github.com/anthropics/anthropic-sdk-java/blob/main/anthropic-java-core/src/main/kotlin/com/anthropic/models/beta/AnthropicBeta.kt) that is not available. 