fix: continued moving everything to orderedmaps plus cleaned up most the tests

datamodel/high/v2/header.go

@@ -6,6 +6,8 @@ package v2
 import (
 	"github.com/pb33f/libopenapi/datamodel/high"
 	low "github.com/pb33f/libopenapi/datamodel/low/v2"
+	"github.com/pb33f/libopenapi/orderedmap"
+	"gopkg.in/yaml.v3"
 )
 
 // Header Represents a high-level Swagger / OpenAPI 2 Header object, backed by a low-level one.
@@ -30,7 +32,7 @@ type Header struct {
 	UniqueItems      bool
 	Enum             []any
 	MultipleOf       int
-	Extensions       map[string]any
+	Extensions       *orderedmap.Map[string, *yaml.Node]
 	low              *low.Header
 }