[JS] Tools should be executable

[maxl0rd]

Tools should be executable.

I want to:

const peepTool = ai.defineTool(...);
// and then somewhere later
await peepTool();

But I get the dreaded

Error: getRegistryInstance() called before runWithRegistry()

Runtime (please complete the following information):

• OS: MacOS
• Version [e.g. 22]

** Node version

• v20.15.1

On Getkit next branch.

[maxl0rd]

Should be fixed by #1091