route: merge rule_set branches into outer rules

Treat rule_set items as merged branches instead of standalone boolean
sub-items.

Evaluate each branch inside a referenced rule-set as if it were merged
into the outer rule and keep OR semantics between branches. This lets
outer grouped fields satisfy matching groups inside a branch without
introducing a standalone outer fallback or cross-branch state union.

Keep inherited grouped state outside inverted default and logical
branches. Negated rule-set branches now evaluate !(...) against their
own conditions and only reapply the outer grouped match after negation
succeeds, so configs like outer-group && !inner-condition continue to
work.

Add regression tests for same-group merged matches, cross-group and
extra-AND failures, DNS merged-branch behaviour, and inverted merged
branches. Update the route and DNS rule docs to clarify that rule-set
branches merge into the outer rule while keeping OR semantics between
branches.

docs/configuration/route/rule.md

@@ -199,7 +199,7 @@ icon: material/new-box
     (`source_port` || `source_port_range`) &&  
     `other fields`
 
-    Additionally, included rule-sets can be considered merged rather than as a single rule sub-item.
+    Additionally, each branch inside an included rule-set can be considered merged into the outer rule, while different branches keep OR semantics.
 
 #### inbound