Feature: Only export used types, don't export unused types

Currently, each JSON export always exports all types.

This might lead to some viewers implementing the extension to incorrectly assume that all types always need to be present and have a specified order, which I believe is not the case.

I think it would be great if only the required types for a graph are exported (so if all nodes operate on "float", then only the float type would be exported).

Start by locating the TypeScript JSON export entry point and the code that gathers graph types; inspect how the export currently includes every type. Verify the change with a graph whose nodes use only float, and confirm the JSON contains only the required type definitions.

Written by the indexing model from the issue text.