Use once_cell from async-lock
Resolves #93 by using the OnceCell type found in async-lock. This type allows for blocking operations, just like the once_cell::Lazy type that was used earlier. In addition, async-lock does not bump our MSRV, while once_cell does.
This is a draft PR because smol-rs/async-lock#27 has not yet been released.
Clippy failure is unrelated to this pull request.
Published a new version of async-lock including https://github.com/smol-rs/async-lock/pull/27.
Published a new version of async-lock including smol-rs/async-lock#27.
Alright, I've switched to using the released version of async-lock in this PR, and marked it ready for review.