Use OnceCell for gloo-history

[jplatte]

The BrowserHistory initialization could be optimized / simplified a bit by using OnceCell instead of RefCell<Option<_>>. However, this would raise the MSRV to 1.70. Are you interested in a PR?

[futursolo]

Thank you for the suggestion.

Unlike a Send + Sync static, RefCell<Option<_>> does not have any racing conditions as it will not be able to execute any other code until the init sequence finished executing.

I think the better solution is to use std::cell::LazyCell in which a lazy initialisation is guaranteed to happen once.

Given I cannot see any downside and LazyCell seems to be a better candidate for this use case, I would prefer to wait until LazyCell is stabilised and switch to LazyCell directly.

I will keep this issue open so we can track the stabilisation process of LazyCell.

[jplatte]

OnceCell also guarantees that it's only initialized once, LazyCell is simply a slightly less general but more convenient type on top of OnceCell. Also no race conditions are possible, we are talking about thread_local variables here.