feat: offload JiveXML/JSON parsing to Web Worker to prevent UI freeze

[Shivansh1205]

Problem

JiveXMLLoader.getEventData() runs DOMParser + full XML data extraction synchronously on the main thread. For large ATLAS events with dense track collections, this causes multi-second UI freezes affecting every experiment (ATLAS, CMS, LHCb, TrackML).

Solution — Phase 1: Worker-based parsing

The key insight: parsing + data extraction (expensive) can run in a worker, while Three.js object creation (needs WebGL context) stays on the main thread — but by that point the data is already structured and fast to process.

Changes

• src/workers/event-data-parser.worker.ts — Web Worker that runs DOMParser and all JiveXML data extraction off the main thread, returning plain serialisable objects (no DOM nodes cross the worker boundary). Also handles JSON.parse for future use.

• src/workers/event-data-parser.ts — Promise-based wrapper with automatic synchronous fallback when Worker is unavailable (SSR, older browsers).

• src/loaders/jivexml-loader.ts — getEventData() is now async. Delegates XML parsing to the worker; private build*() methods reconstruct the event data from the plain worker result.

• src/event-display.ts — buildEventDataFromJSON() and loadEvent() are now async.

Considerations addressed

• Workers cannot access DOM/Three.js — only pure data parsing is offloaded
• Fallback to synchronous path if Workers unavailable
• No transferable objects needed (string input, plain object output)
• Phase 2 (chunked progress reporting) can be layered on top of this worker infrastructure

[EdwardMoyse]

This is a bit hard to review because GitHub seems to think that you are adding jivexml-loader.ts and event-display.ts i.e. I cannot easily see the lines you have changed. I'm not sure why. :-/

I will have to look at this more carefully this evening.

[sponce]

This is due to the fact that the new files is not in the right place in the hierarchy. Instead of being in path phoenix/packages/phoenix-event-display/src/loaders/jivexml-loader.ts, where '/' separates the directories, it's in phoenix\/packages\/phoenix-event-display\/src/loaders\/jivexml-loader.ts, meaning there is a directory called phoenix/packages/phoenix-event-display/src t the top level. @Shivansh1205 can you fix this ?

[Shivansh1205]

@sponce i will try doing it by this evening