gh-150490: Raise PyType_Modified for insertion into split dictionary

[DinoV]

When we insert into a split dictionary we update the shared keys version - this is used to invalidate caches for loading methods and loading class values and requires us to check the keys version. Instead we can raise PyType_Modified which lets us rely on the type version check + has inline values check instead of validating that we have the correct keys version. This gets rid of loading the cached keys version, the objects type (although likely the compiler eliminates this already), loading the cached keys from the type, and then loading the keys version and comparing it against the cached value.

• Issue: Raise PyType_Modified on split key insertion to avoid cached keys version check #150490

[markshannon]

The change to the dict and removal of the keys version check seems good, but why have you removed several seemingly unrelated tests?

[markshannon]

Why not pass the kind directly, instead of a bool?

[DinoV]

It's not actually changed the diff is just doing a bad job of seeing that part of this was pulled into init_keys_object so it's showing this both deleted and added. But the callers tend to have. the bool value already in hand and new_keys_object seems to want to do a couple of truthy checks so I think it makes sense.

[markshannon]

I was hoping that #142889 would be implemented first, but it looks like progress there has stalled.

So, let's merge this.