feat!: Hugrmut on generic nodes (#2111)

- Allows `HugrMut` to be implemented for `HugrView`s with arbitrary node
types
- Removes `HugrMutInternals::hugr_mut(&mut self) -> &mut Hugr`, it can
be implemented for more complex types. This is required for #1926, but I
haven't touched the read-only side yet.
- Added a `Node` associated type to `Rewrite`. All existing rewrites
only implement `Rewrite<Node = Node>` for now, expanding their type is
left for a separate PR.

drive-by: Fix a couple bugs in rewrite implementations that assumed that
`SiblingMut` contained transitive children.

BREAKING CHANGE: `HugrMut` is now implemented generically for any
`HugrView::Node` type.
BREAKING CHANGE: `SiblingMut` has a new type parameter for the wrapped
hugr type.

Author: aborgna-q

hugr-core/src/builder/build_traits.rs

@@ -153,7 +153,7 @@ pub trait Container {
     where
         ExtensionRegistry: Extend<Reg>,
     {
-        self.hugr_mut().extensions_mut().extend(registry);
+        self.hugr_mut().use_extensions(registry);
     }
 }