feat: add ToolRegistry.clone() and replace() for per-session registries

src/sandbox/index.ts

@@ -0,0 +1,3 @@
+export { DockerSandbox, type DockerSandboxConfig, type ExecOptions, type ExecResult } from './docker.js';
+export { SandboxManager } from './manager.js';
+export { createSandboxedShellTool, createSandboxedProcessStartTool } from './tools.js';