skiplist: add compare_insert

[Tianion]

The purpose is support compare and swap / compare and exchange.
I notice that the function insert_internal is core function, so I change replace to support CAS

[Tianion]

hhh...CI / san (pull_request) Cancelled after 360m. There seems no problem with this commit
example

let map = SkipMap::new();
map.insert("key", 1);
map.compare_insert("key", 0, |x| x < &0);
assert_eq!(*map.get("key").unwrap().value(), 1);
map.compare_insert("key", 2, |x| x < &2);
assert_eq!(*map.get("key").unwrap().value(), 2);

[taiki-e]

Thanks for the PR! CI failure should be fixed by rebasing.

[taiki-e]

Could you also add a test for a case where the key is not present? (should work the same as insert)

Also, it would be nice to clarify in the documentation that the closure will not be called if the key is not present.

[Tianion]

The rustc version in the CI has been upgraded from 1.71 to 1.72, which resulted in CI/Clippy checks failing. I attempted to fix it, but there are certain issues below that I'm unsure how to address.
As a workaround, I had to use #[allow(clippy::arc_with_non_send_sync)] to pass the CI/clippy. I tried replacing Arc with Rc, but this would likely introduce other problems.

error: usage of an `Arc` that is not `Send` or `Sync`
  --> crossbeam-epoch/src/collector.rs:32:21
   |
32 |             global: Arc::new(Global::new()),
   |                     ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: the trait `Sync` is not implemented for `Global`
   = note: required for `Arc<Global>` to implement `Send` and `Sync`
   = help: consider using an `Rc` instead or wrapping the inner type with a `Mutex`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#arc_with_non_send_sync
   = note: `-D clippy::arc-with-non-send-sync` implied by `-D warnings`

[taiki-e]

Could you remove (or revert) clippy-related commits? They have been addressed in #1021.

[Tianion]

Could you remove (or revert) clippy-related commits? They have been addressed in #1021.

Done，thanks for your detailed review

[taiki-e]

Thanks!