Add support for atomic min and max

[mppf]

This PR adds support for atomic min and max. While there is an expectation that these signatures can be stable, this PR adds them as unstable for now.

See issue #22867 which requests this functionality.

What do other languages do here?

• C++ has a proposal https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p0493r5.pdf which adds atomic_fetch_min / atomic_fetch_max (and also _explicit variants of these to allow providing the memory order).
• Rust has fetch_min and fetch_max (see e.g. https://doc.rust-lang.org/std/sync/atomic/struct.AtomicU32.html#method.fetch_max)

Future Work:

• add NetworkAtomics versions of these

• [ ] full comm=none testing
• [ ] add chpldoc docs comments