#2428 Checkpoint using latest Magistrate trait-based API

[Matthew-Whitlock]

Closes #2428

This also enables recovering to the same proxy ID as checkpointed, when possible. Some additional minor convenience features used for resilience are also included, like getting the index from a collection element proxy and getting the objgroup proxy from an objgroup element proxy.

[github-actions]

clang-format output for this changeset:

diff --git a/src/vt/vrt/proxy/collection_elm_proxy.impl.h b/src/vt/vrt/proxy/collection_elm_proxy.impl.h
index b0608db72..586ecd72b 100644
--- a/src/vt/vrt/proxy/collection_elm_proxy.impl.h
+++ b/src/vt/vrt/proxy/collection_elm_proxy.impl.h
@@ -106,8 +106,8 @@ void VrtElmProxy<ColT, IndexT>::serialize(SerT& s) {
         //then immediately deserialize
         using listener::ElementEventEnum;
         listener::ListenFnType<IndexT> m_listener =
-          [*this, buf, listener_id]
-          (ElementEventEnum event, IndexT idx, NodeType) mutable {
+          [*this, buf,
+           listener_id](ElementEventEnum event, IndexT idx, NodeType) mutable {
             if (!(idx == getIndex()))
               return;
             if (event != ElementEventEnum::ElementMigratedIn)

[PhilMiller]

Is setTraits() actually just getting s with an empty set of traits, or is it mutating s itself? This looks like either mis-use, or mis-naming.

[Matthew-Whitlock]

This is getting s with an empty set of traits. The traits are immutable, since they're types. I can see how the naming may be misleading, but setTraits() (which gets a serializer with only the specified traits) needs to be distinct from withTraits() and withoutTraits() (which get serializers with the specified traits added-to/removed-from the existing traits). Happy to rename if you have any suggestions, but that'd be a PR in Magistrate

[Matthew-Whitlock]

asTraits() seems a little clearer