refactor: rename files to follow Go convention

testdata/unused_receiver_custom_regex.go

@@ -0,0 +1,12 @@
+package fixtures
+
+// all will ok with xxxParam if Arguments = [{allowRegex="^xxx"}]
+
+func (xxxParam *SomeObj) f0() {}
+
+// still works with _
+
+func (_ *SomeObj) f1() {}
+
+func (yyyParam *SomeObj) f2() { // MATCH /method receiver 'yyyParam' is not referenced in method's body, consider removing or renaming it to match ^xxx/
+}