khepri_tree: Use an intermediate parameterized type on top of #tree{}

[Why]
Our `#tree{}` type has two versions which differ on the type of the
`keep_while_conds_revidx` field. We also defined two type, `tree_v0()`
and `tree_v1()` which finished to define the two versions.

This was fine up to and including Erlang/OTP 27. However with Erlang/OTP
28, Dialyzer complained that `update_keep_while_conds/3` would never
return.

This was caused by the new "nominal type" property of opaque types: if I
understand correclty, based on the type specs, we couldn't modify the
`#tree{}` record in `update_keep_while_conds/3` because the returned
`#tree{}` might not be a `tree_v0()` or a `tree_v1()`.

[How]
In the end, we couldn't use the #tree{} record directly to define the
`tree_v0()` and `tree_v1()` types. We have to use an intermediate type
that takes the type of the `keep_while_conds_revidx` field, then use
this intermediate type in the definition of `tree_v0()` and `tree_v1()`.

We remove the type of the `keep_while_conds_revidx` field in the record
because it breaks the compilation with Erlang/OTP 27.

Author: dumbbell

src/khepri_tree.erl

@@ -40,16 +40,16 @@
 
 -record(tree, {root = #node{} :: khepri_tree:tree_node(),
                keep_while_conds = #{} :: khepri_tree:keep_while_conds_map(),
-               keep_while_conds_revidx = #{} ::
-               khepri_tree:keep_while_conds_revidx()}).
+               keep_while_conds_revidx = #{}}).
 
 -type tree_node() :: #node{}.
 %% A node in the tree structure.
 
--opaque tree_v0() :: #tree{keep_while_conds_revidx ::
-                           khepri_tree:keep_while_conds_revidx_v0()}.
--opaque tree_v1() :: #tree{keep_while_conds_revidx ::
-                           khepri_tree:keep_while_conds_revidx_v1()}.
+-type tree(KeepWhileCondsRevIdxType) :: #tree{keep_while_conds_revidx ::
+                                              KeepWhileCondsRevIdxType}.
+
+-opaque tree_v0() :: tree(khepri_tree:keep_while_conds_revidx_v0()).
+-opaque tree_v1() :: tree(khepri_tree:keep_while_conds_revidx_v1()).
 
 -type tree() :: tree_v0() | tree_v1().
 
@@ -389,10 +389,16 @@ is_keep_while_condition_met_on_self(
             true
     end.
 
+-spec update_keep_while_conds(Tree, Watcher, KeepWhile) -> NewTree when
+      Tree :: khepri_tree:tree(),
+      Watcher :: khepri_path:native_path(),
+      KeepWhile :: khepri_condition:native_keep_while(),
+      NewTree :: khepri_tree:tree().
+
 update_keep_while_conds(Tree, Watcher, KeepWhile) ->
     AbsKeepWhile = to_absolute_keep_while(Watcher, KeepWhile),
     Tree1 = update_keep_while_conds_revidx(Tree, Watcher, AbsKeepWhile),
-    #tree{keep_while_conds = KeepWhileConds} = Tree1,
+    KeepWhileConds = get_keep_while_conds(Tree1),
     KeepWhileConds1 = KeepWhileConds#{Watcher => AbsKeepWhile},
     Tree1#tree{keep_while_conds = KeepWhileConds1}.