✨ Async Multithreading

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Suggestion

ther are many processes that would benefit from async multithreading support in the core library like precompute buffers (#216) and ballot encryption. This issue is to example the possiblity of adding back in support for asynchronous multithreaded selection encryption and other loops. Specific attention should be paid to ensuring things are threadsafe (using async locks and queues) and that they work well with wasm/web workers.

### Possible Implementation

_No response_

### Anything else?

_No response_

Start by reading the core library's selection-encryption and other loop implementations, then review issue #216 on precompute buffers. Assess how async locks, queues, and WASM/web workers could support multithreading while remaining thread-safe; done requires an agreed design and working coverage for the affected operations.

Written by the indexing model from the issue text.