Tracking issue for `once_lazy_lock_get_unchecked`

Feature gate: #![feature(once_lazy_lock_get_unchecked)]

This is a tracking issue for the get_unchecked methods on OnceLock and
LazyLock.

The original implementation PR (#138914) was closed due to inactivity. Since
the ACP has been accepted and there is currently no active implementation PR,
this tracking issue is being opened to track the feature.

Public API

impl<T, F> LazyLock<T, F> {
    pub unsafe fn get_unchecked(this: &Self) -> &T;
    pub unsafe fn get_unchecked_mut(this: &mut Self) -> &mut T;
}
impl<T> OnceLock<T> {
    pub unsafe fn get_unchecked(&self) -> &T;
    pub unsafe fn get_unchecked_mut(&mut self) -> &mut T;
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• ACP: rust-lang/libs-team#654
• Implementation: #138914 (closed due to inactivity)
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• None yet.

Start with the listed public API and the accepted ACP in rust-lang/libs-team#654; the issue names no implementation files or tests. Review the closed implementation PR #138914 and the feature lifecycle requirements, then determine the implementation and testing scope. Done means the methods are implemented, reviewed through FCP, and have a stabilization PR.