Function create_runtime 

pub fn create_runtime(
    dispatcher: Option<Arc<dyn ToolDispatcher>>,
    max_heap_size: usize,
    tool_call_limits: Option<ToolCallLimits>,
) -> Result<JsRuntime, SandboxError>

Create a fresh JsRuntime with the forge extension loaded and V8 heap limits set.

Public for reuse in the worker binary.