refactor(worker-threads): pass functions as strings to resolve Promise cloning issues

- Updated worker execution logic to pass functions as stringified versions instead of reference types to avoid cloning issues in worker threads.
- Refactored utility functions in `workerUtils` to accept serialized function strings.
- Adjusted embedding and augmentation pipeline workflows to align with the updated worker handling mechanism.
- Enhanced parallel distance calculator to support structured arguments with stringified distance functions for better compatibility.

src/pipeline.ts

@@ -418,7 +418,7 @@ export class Pipeline implements IPipeline {
                 return augFn.apply(augmentation, workerArgs)
               }
 
-              methodPromise = executeInThread<AugmentationResponse<T>>(workerFn, ...args)
+              methodPromise = executeInThread<AugmentationResponse<T>>(workerFn.toString(), args)
             } catch (threadError) {
               console.warn(`Failed to execute in thread, falling back to main thread: ${threadError}`)
               // Fall back to executing in the main thread