fix: don't mutate contexts

lib/ParsingContext.ts

@@ -207,7 +207,7 @@ export class ParsingContext {
           || scopedContext[key]['@context']['@propagate']; // Propagation is true by default
 
         if (propagate !== false || i === keysOriginal.length - 1 - offset) {
-          contextRaw = scopedContext;
+          contextRaw = { ...scopedContext };
 
           // Clean up final context
           delete contextRaw['@propagate'];

lib/entryhandler/keyword/EntryHandlerKeywordType.ts

@@ -69,18 +69,16 @@ export class EntryHandlerKeywordType extends EntryHandlerKeyword {
     if (hasTypedScopedContext) {
       // Do not propagate by default
       scopedContext = scopedContext.then((c) => {
-        if (!('@propagate' in c.getContextRaw())) {
-          c.getContextRaw()['@propagate'] = false;
-        }
+        let rawContext = c.getContextRaw();
 
         // Set the original context at this depth as a fallback
         // This is needed when a context was already defined at the given depth,
         // and this context needs to remain accessible from child nodes when propagation is disabled.
-        if (c.getContextRaw()['@propagate'] === false) {
-          c.getContextRaw()['@__propagateFallback'] = context.getContextRaw();
+        if (rawContext['@propagate'] !== true) {
+          rawContext = { ...rawContext, '@propagate': false, '@__propagateFallback': context.getContextRaw() };
         }
 
-        return c;
+        return new JsonLdContextNormalized(rawContext);
       });
 
       // Set the new context in the context tree