feat(context): null-prototype scope frames via createScope (#899)

- Add createScope() building Object.create(null) with optional own props

- Initialize context stack bottom with createScope() for assign/capture

- Push null-proto scopes from for, tablerow, block, layout, include (incl. Jekyll)

Co-authored-by: Cursor <[email protected]>

src/context/scope.ts

@@ -1,7 +1,13 @@
 import { Drop } from '../drop/drop'
 
-interface ScopeObject extends Record<string | number | symbol, any> {
+export interface ScopeObject extends Record<string | number | symbol, any> {
   toLiquid?: () => any;
 }
 
 export type Scope = ScopeObject | Drop
+
+export function createScope (from?: ScopeObject): ScopeObject {
+  const scope = Object.create(null)
+  if (from) Object.assign(scope, from)
+  return scope
+}