fix!: Don't expose HugrMutInternals (#2071)

`HugrMutInternals` is part of the semi-private traits defined in
`hugr-core`.
While most things get re-exported in `hugr`, we `*Internal` traits
require you to explicitly declare a dependency on the `-core` package
(as we don't want most users to have to interact with them).

For some reason there was a public re-export of the trait in a
re-exported module, so it ended up appearing in `hugr` anyways.

BREAKING CHANGE: Removed public re-export of `HugrMutInternals` from
`hugr`.

Author: aborgna-q

hugr-core/src/hugr/rewrite/simple_replace.rs

@@ -4,7 +4,6 @@ use std::collections::HashMap;
 
 use crate::core::HugrNode;
 use crate::hugr::hugrmut::InsertionResult;
-pub use crate::hugr::internal::HugrMutInternals;
 use crate::hugr::views::SiblingSubgraph;
 use crate::hugr::{HugrMut, HugrView, Rewrite};
 use crate::ops::{OpTag, OpTrait, OpType};