feat: Add async LazyLock implementation

[mhambre]

Adds support for an asynchronousLazyLock inspired by async-lazy and similarly the API provided by std::sync::LazyLock.

The main addition to this is the fallible initialization through LazyLock::try_force and being runtime agnostic (async-lazy is married to Tokio through sync primitives) by using asyncband's Mutex and OnceCell.

Some design choices:

• Cancelled futures restart rather than continuing polling from the cancellation point. This choice is subject to discussion and could also be implemented in the future if decided.
• Panics in the initializer poison the lock.
• Keeping with the API of std::sync::LazyLock, get methods are introspective, force methods actively perform initialization.
• Deref traits aren't implemented because you can't await a deref.

This implementation is in reference to #160.

[tisonkun]

Thanks for your contribution @mhambre! Feel free to ping me when this PR is ready for review.