Refactor and enhance type safety across various modules

- Updated function parameters and return types in `page-preview.ts`, `pdf-decrypt.ts`, and `pymupdf-loader.ts` for improved type safety.
- Introduced type definitions for `CpdfInstance`, `PyMuPDFInstance`, and other related types to ensure better type checking.
- Enhanced error handling in `sanitize.ts` by creating a utility function for error messages.
- Removed unnecessary type assertions and improved type inference in `editor.ts`, `serialization.ts`, and `tools.test.ts`.
- Added type definitions for markdown-it plugins to improve compatibility and type safety.
- Enforced stricter TypeScript settings by enabling `noImplicitAny` in `tsconfig.json`.
- Cleaned up test files by refining type assertions and ensuring consistency in type usage.

src/tests/watermark.test.ts

@@ -61,7 +61,7 @@ describe('Watermark Feature', () => {
     });
 
     it('should reset pdfDoc to null', () => {
-      state.pdfDoc = {} as any;
+      state.pdfDoc = {} as unknown as typeof state.pdfDoc;
 
       resetState();
 
@@ -69,7 +69,7 @@ describe('Watermark Feature', () => {
     });
 
     it('should reset pdfPages array', () => {
-      state.pdfPages = [1, 2, 3] as any;
+      state.pdfPages = [1, 2, 3] as unknown as typeof state.pdfPages;
 
       resetState();