Modernize with async/await and internal library loading

[zachthedev]

• Converted PDFApp to use async/await for all core operations.
• Refactored library loading (pdf-lib, fontkit) to be managed within each PDFApp instance, restoring original helper method functionality.
• Improved state handling for top-level chained calls.

[gemini-code-assist]

Summary of Changes

Hello @zachthedev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request modernizes the PDFApp class by adopting async/await for asynchronous operations, leading to cleaner and more readable code. It also significantly changes how external libraries (pdf-lib, fontkit) are managed, making them instance-specific dependencies rather than global ones. Additionally, internal state management for chained method calls has been refined.

Highlights

• Async/Await Conversion: Converted most public and internal methods within the PDFApp class to use async/await for handling asynchronous operations, moving away from explicit Promise constructors in many cases.
• Library Loading Refactor: Refactored the loading of pdf-lib and fontkit libraries. Instead of being loaded globally/statically, they are now loaded asynchronously on demand via new _ensurePdfLibLoaded and _ensureFontkitLoaded functions and passed into the PDFApp constructor, making library dependencies instance-specific.
• State Management: Improved state handling for chained calls by consolidating configuration options (useStandardFont, useCustomFont) into a _gPDFA_Config object and renaming the internal PDF blob storage from pdfBlob to _gPDFA_Blob.

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[gemini-code-assist]

Code Review

This pull request modernizes the PDFApp library by migrating to async/await, enhancing code readability and maintainability. The refactoring of library loading (pdf-lib, fontkit) and injection into PDFApp instances is a solid architectural improvement.

Several critical issues need addressing, primarily missing await keywords for asynchronous operations which will lead to runtime errors. There's also a syntax error and a high-risk setTimeout override that requires careful consideration. Once these are resolved, the changes will greatly improve the library.