fix: Update Doxyfile and ensure output directory exists

This commit addresses issues found during Doxygen generation:

- Upgraded `Doxyfile` to version 1.9.8 using `doxygen -u` to remove obsolete tags and ensure compatibility.
- Modified the `.github/workflows/analysis.yml` workflow to add a step that creates the `docs/doxygen` output directory before Doxygen is run. This resolves the "Output directory does not exist" error.

Author: google-labs-jules[bot]

.github/workflows/analysis.yml

@@ -21,6 +21,9 @@ jobs:
     - name: Install Doxygen
       run: sudo apt-get update && sudo apt-get install -y doxygen
 
+    - name: Create Doxygen Output Directory
+      run: mkdir -p docs/doxygen
+
     - name: Generate Doxygen Documentation
       run: doxygen Doxyfile