khepri_machine: Fix comparison between opaque khepri_machine:state() terms

[Why]
`khepri_machine:state()` can be either a `state_v0()` or a `state_v1()`
which are both opaque types. Therefore, they can't simply be compared
with =:= because it violates the contract that a e.g. a `state_v0()`
can't be compared to a `state_v1()` without knowing their internals.

This was reported by Dialyzer in Erlang/OTP 28.

[How]
We add an assert function to both `khepri_machine` and
`khepri_machine_v0`. They can inspect their respective version of the
state because they define it.

Author: dumbbell

src/khepri_machine.erl

@@ -520,9 +520,10 @@ readonly_transaction(StoreId, Fun, Args, Options)
                     %% It is a read-only transaction, therefore we assert that
                     %% the state is unchanged and that there are no side
                     %% effects.
-                    {State, Ret, []} = khepri_tx_adv:run(
-                                         State, Fun, Args, false,
-                                         Meta),
+                    {State1, Ret, []} = khepri_tx_adv:run(
+                                          State, Fun, Args, false,
+                                          Meta),
+                    assert_equal(State, State1),
                     Ret
             end,
     case process_query(StoreId, Query, Options) of
@@ -537,9 +538,10 @@ readonly_transaction(StoreId, PathPattern, Args, Options)
                     %% It is a read-only transaction, therefore we assert that
                     %% the state is unchanged and that there are no side
                     %% effects.
-                    {State, Ret, []} = locate_sproc_and_execute_tx(
-                                         State, PathPattern, Args, false,
-                                         Meta),
+                    {State1, Ret, []} = locate_sproc_and_execute_tx(
+                                          State, PathPattern, Args, false,
+                                          Meta),
+                    assert_equal(State, State1),
                     Ret
             end,
     case process_query(StoreId, Query, Options) of
@@ -2634,6 +2636,16 @@ get_store_id(State) ->
     #config{store_id = StoreId} = get_config(State),
     StoreId.
 
+-spec assert_equal(State1, State2) -> ok when
+      State1 :: khepri_machine:state(),
+      State2 :: khepri_machine:state().
+
+assert_equal(#khepri_machine{} = State1, #khepri_machine{} = State2) ->
+    ?assertEqual(State1, State2),
+    ok;
+assert_equal(State1, State2) ->
+    khepri_machine_v0:assert_equal(State1, State2).
+
 -ifdef(TEST).
 -spec make_virgin_state(Params) -> State when
       Params :: khepri_machine:machine_init_args(),

src/khepri_machine_v0.erl

@@ -13,6 +13,8 @@
 
 -module(khepri_machine_v0).
 
+-include_lib("stdlib/include/assert.hrl").
+
 -include("src/khepri_machine.hrl").
 
 -export([init/1]).
@@ -25,6 +27,7 @@
          get_emitted_triggers/1, set_emitted_triggers/2,
          get_projections/1, set_projections/2,
          get_metrics/1, set_metrics/2,
+         assert_equal/2,
          state_to_list/1]).
 
 -record(khepri_machine,
@@ -191,6 +194,7 @@ get_metrics(#khepri_machine{metrics = Metrics}) ->
 set_metrics(#khepri_machine{} = State, Metrics) ->
     State#khepri_machine{metrics = Metrics}.
 
+
 -spec state_to_list(State) -> Fields when
       State :: khepri_machine_v0:state(),
       Fields :: [any()].
@@ -200,3 +204,11 @@ set_metrics(#khepri_machine{} = State, Metrics) ->
 
 state_to_list(#khepri_machine{} = State) ->
     tuple_to_list(State).
+
+-spec assert_equal(State1, State2) -> ok when
+      State1 :: khepri_machine:state(),
+      State2 :: khepri_machine:state().
+
+assert_equal(#khepri_machine{} = State1, #khepri_machine{} = State2) ->
+    ?assertEqual(State1, State2),
+    ok.