use parking_lot

[cssivision]

No description provided.

[ghost]

Are there any significant improvements in benchmarks? I feel hesitant about adding a new dependency if not.

[raftario]

Could this be made into an optional feature while defaulting to the standard library ?

[raftario]

As of performance improvements, the main one is that parking_lot::Condvar is a lot cheaper to create compared to std::sync::Condvar cause the latter allocates.

[taiki-e]

I'm okay with adding this as an optional feature, but I'd like to know how much this actually improves performance before merging. (I know parking_lot is basically faster than std, but switching to it doesn't necessarily help improve overall performance.)

[taiki-e]

Closing -- std mutex enough fast since rust-lang/rust#95035