khepri_path, khepri_tree: Fix a few specs' return value

[Why]
There are several functions which use the same variable as an argument
and as their return value in their spec. Semantically, this means that
the argument is returned as is. Dialyzer doesn't enforce anything with
that (yet). But this is still incorrect.

So while working on several warnings, fix a few function specs. There
are still other functions that are incorrect in the same way.

Author: dumbbell

src/khepri_path.erl

@@ -625,8 +625,9 @@ abspath([_ | _] = RelativePath, BasePath) ->
 abspath([] = PathToRoot, _) ->
     PathToRoot.
 
--spec realpath(Path) -> Path when
-      Path :: native_pattern().
+-spec realpath(Path) -> NewPath when
+      Path :: native_pattern(),
+      NewPath :: native_pattern().
 
 realpath(Path) ->
     realpath(Path, []).

src/khepri_tree.erl

@@ -321,9 +321,10 @@ squash_version_bumps_after_keep_while(
 %% Keep-while functions.
 %% -------------------------------------------------------------------
 
--spec to_absolute_keep_while(BasePath, KeepWhile) -> KeepWhile when
+-spec to_absolute_keep_while(BasePath, KeepWhile) -> AbsKeepWhile when
       BasePath :: khepri_path:native_path(),
-      KeepWhile :: khepri_condition:native_keep_while().
+      KeepWhile :: khepri_condition:native_keep_while(),
+      AbsKeepWhile :: khepri_condition:native_keep_while().
 %% @private
 
 to_absolute_keep_while(BasePath, KeepWhile) ->
@@ -395,11 +396,11 @@ update_keep_while_conds(Tree, Watcher, KeepWhile) ->
     KeepWhileConds1 = KeepWhileConds#{Watcher => AbsKeepWhile},
     Tree1#tree{keep_while_conds = KeepWhileConds1}.
 
--spec update_keep_while_conds_revidx(Tree, Watcher, KeepWhile) ->
-    Tree when
+-spec update_keep_while_conds_revidx(Tree, Watcher, KeepWhile) -> NewTree when
       Tree :: tree(),
       Watcher :: khepri_path:native_path(),
-      KeepWhile :: khepri_condition:native_keep_while().
+      KeepWhile :: khepri_condition:native_keep_while(),
+      NewTree :: tree().
 
 update_keep_while_conds_revidx(
   #tree{keep_while_conds_revidx = KeepWhileCondsRevIdx} = Tree,