Wasm support

Is your feature request related to a problem? Please describe.
This project is ultimately intended to be used by Asteracea, which should also run as web frontend framework, but it uses async-lock's OnceCell in a way that's not supported there.

Describe the solution you'd like
The implementation has to be adjusted somehow to avoid "once.set_blocking", or a different (or no) library may have to be used.

Describe alternatives you've considered
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