Refactor PdfEngine to use queued task orchestration

Refactors PdfEngine and related orchestrator code to enqueue all PDF operations through a WorkerTaskQueue, ensuring serialized and prioritized execution. Removes legacy encoder pool logic and introduces CompoundTask for aggregating multi-page operations such as annotation and search. Updates type signatures and progress reporting for improved consistency and extensibility. Adds CompoundTask utility to models for advanced task composition.

Author: bobsingor

packages/engines/src/lib/orchestrator/pdf-engine.ts

@@ -47,7 +47,6 @@ type MessageType =
   | 'initialize'
   | 'destroy'
   | 'openDocumentBuffer'
-  | 'openDocumentFromLoader'
   | 'getMetadata'
   | 'setMetadata'
   | 'getDocPermissions'
@@ -226,10 +225,6 @@ export class RemoteExecutor implements IPdfExecutor {
     return this.send<PdfDocumentObject>('openDocumentBuffer', [file, options]);
   }
 
-  openDocumentFromLoader(fileLoader: any, password?: string): PdfTask<PdfDocumentObject> {
-    return this.send<PdfDocumentObject>('openDocumentFromLoader', [fileLoader, password]);
-  }
-
   getMetadata(doc: PdfDocumentObject): PdfTask<PdfMetadataObject> {
     return this.send<PdfMetadataObject>('getMetadata', [doc]);
   }