fix: move model construction off the JS thread

[yocontra]

Problem

The loadModel template in RnExecutorchInstaller.h constructs model objects synchronously on the JS thread. For models like Kokoro TTS, the constructor loads .pte files, initializes the phonemizer, and reads voice data — blocking the JS thread for several seconds.

This prevents React from rendering any pending state updates (loading spinners, progress indicators, etc.) until construction completes. For example, calling setIsSynthesizing(true) followed by tts.load() will not show the loading UI for 3-4 seconds because the JS thread is blocked by the synchronous native constructor.

Solution

Make loadModel return a Promise and dispatch the heavy model construction to GlobalThreadPool::detach — matching the pattern already used by promiseHostFunction for inference calls like generate().

C++ (RnExecutorchInstaller.h)

• JSI arguments are still parsed on the JS thread (required for jsi::Value access)
• Model construction is dispatched to GlobalThreadPool::detach
• The Promise resolves on the JS thread via callInvoker->invokeAsync with the host object
• Error handling follows the same pattern as promiseHostFunction in ModelHostObject.h

TypeScript

• All global.load*() call sites updated to await the now-async result
• Global type declarations updated to return Promise<any>
• SpeechToText already used await, so no change needed there

Breaking Change

This is a breaking change for any consumers calling global.load*() directly and expecting a synchronous return value. However:

• The public module APIs (load() methods) are already async — no user-facing API changes needed
• The global.load*() functions are internal/undocumented

Test Plan

• Verify model loading still works for all model types (TTS, LLM, OCR, etc.)
• Verify that React state updates (loading spinners) render immediately when load() is called, rather than being delayed until construction completes
• Verify error handling still propagates correctly from native construction failures

[msluszniak]

There is an error in CI build, specifically in VerticalOCR, I guess we just need to mark it as promise like for the other models.

[yocontra]

@msluszniak Fixed! I can't see the CI but pretty sure I made the correct changes.

[msluszniak]

Cool now all important checks work. Now, we just need to fix lint, I will fix this for you later today and then proceed with the actual review ;)

[yocontra]

@msluszniak Fixed the lint errors - my bad

[msluszniak]

FYI @yocontra, I will push changes to the API reference so CI will pass. Other then that, I tested changes and everything was correct. :))

[msluszniak]

🚀

[chmjkb]

Thanks for another contribution @yocontra 🫶, I will perform some quality checks tomorrow and then I think we're ready to merge :)