fix: replace checker.NewMapIterator with newMapIterator for HTTPHeaders and URLValues

Signed-off-by: Jason Cameron <jason.cameron@stanwith.me>

lib/policy/expressions/url_values.go

@@ -1,19 +1,15 @@
 package expressions
 
 import (
-	"errors"
 	"net/url"
 	"reflect"
 	"strings"
 
-	"github.com/TecharoHQ/anubis/lib/policy/checker"
 	"github.com/google/cel-go/common/types"
 	"github.com/google/cel-go/common/types/ref"
 	"github.com/google/cel-go/common/types/traits"
 )
 
-var ErrNotImplemented = errors.New("expressions: not implemented")
-
 // URLValues is a type wrapper to expose url.Values into CEL programs.
 type URLValues struct {
 	url.Values
@@ -71,7 +67,7 @@ func (u URLValues) Get(key ref.Val) ref.Val {
 }
 
 func (u URLValues) Iterator() traits.Iterator {
-	return checker.NewMapIterator(u.Values)
+	return newMapIterator(u.Values)
 }
 
 func (u URLValues) IsZeroValue() bool {