khepri_import_export: Fix comparison between opaque khepri_tree:tree() terms

[Why]
`khepri_tree:tree()` can be either a `tree_v0()` or a `tree_v1()` which
are both opaque types. Therefore, they can't simply be compared with =:=
because it violates the contract that a e.g. a `tree_v0()` can't be
compared to a `tree_v1()` without knowing their internals.

This was reported by Dialyzer in Erlang/OTP 28.

[How]
We move the assert to `khepri_tree` which defines these opaque types and
thus has the right to compare them.

Author: dumbbell

src/khepri_import_export.erl

@@ -239,7 +239,7 @@ do_export(State, PathPattern, Module, ModulePriv) ->
                      Tree, PathPattern, TreeOptions, Fun, ModulePriv1),
             case Ret1 of
                 {ok, Tree1, _AppliedChanges, FinalModulePriv} ->
-                    ?assertEqual(Tree, Tree1),
+                    khepri_tree:assert_equal(Tree, Tree1),
                     commit_write(Module, FinalModulePriv);
                 {error, _} = Error ->
                     Error

src/khepri_tree.erl

@@ -22,6 +22,7 @@
 -export([new/0,
          get_root/1,
          get_keep_while_conds/1,
+         assert_equal/2,
 
          are_keep_while_conditions_met/2,
 
@@ -125,6 +126,14 @@ get_root(#tree{root = Root}) ->
 get_keep_while_conds(#tree{keep_while_conds = KeepWhileConds}) ->
     KeepWhileConds.
 
+-spec assert_equal(Tree1, Tree2) -> ok when
+      Tree1 :: khepri_tree:tree(),
+      Tree2 :: khepri_tree:tree().
+
+assert_equal(#tree{} = Tree1, #tree{} = Tree2) ->
+    ?assertEqual(Tree1, Tree2),
+    ok.
+
 -spec create_node_record(Payload) -> Node when
       Payload :: khepri_payload:payload(),
       Node :: tree_node().