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/dns/rule.zh.md

@@ -208,7 +208,7 @@ icon: material/alert-decagram
     (`source_port` || `source_port_range`) &&  
     `other fields`
 
-    另外，引用的规则集可视为被合并，而不是作为一个单独的规则子项。
+    另外，引用规则集中的每个分支都可视为与外层规则合并，不同分支之间仍保持 OR 语义。
 
 #### inbound
 
@@ -550,4 +550,4 @@ Available values: `wifi`, `cellular`, `ethernet` and `other`.
 
 ==必填==
 
-包括的规则。
+包括的规则。