feat: Add HugrMut::insert(_view)_forest (#2518)

closes #2500, #2496

* New trait methods can insert several subtrees at once at different
locations in target Hugr
* trait-default-implement `insert_hugr`, `insert_view` and
`insert_subgraph` using these

Technically I think this is breaking, any external `impl HugrMut` now
has to provide these new methods, but we believe implementations of
HugrMut outside of hugr-core to be sufficiently rare not to justify a
major-version-number release, and rs-semver-checks does not seem to pick
up on this.

Author: acl-cqc

hugr-core/src/builder/build_traits.rs

@@ -99,6 +99,9 @@ pub trait Container {
     }
 
     /// Insert a copy of a HUGR as a child of the container.
+    ///
+    /// Only the portion below the entrypoint will be inserted, with any incoming
+    /// edges broken.
     fn add_hugr_view<H: HugrView>(&mut self, child: &H) -> InsertionResult<H::Node, Node> {
         let parent = self.container_node();
         self.hugr_mut().insert_from_view(parent, child)
@@ -256,7 +259,9 @@ pub trait Dataflow: Container {
     }
 
     /// Copy a hugr-defined op into the sibling graph, wiring up the
-    /// `input_wires` to the incoming ports of the resulting root node.
+    /// `input_wires` to the incoming ports of the node that was the entrypoint.
+    /// (Note, any part of `hugr` outside the entrypoint is not copied;
+    /// this may lead to new input ports being disconnected.)
     ///
     /// # Errors
     ///