Refactor: CitaviXMLImporter to use StAX parser exclusively

[ganesh-vk]

Closes #9539

Refactor: CitaviXMLImporter now uses StAX exclusively, deprecating reliance on JAXB and also improving performance. All tests from CitaviXmlImporterFilesTest pass successfully.

Steps to test

Run CitaviXmlImporterFilesTest or import a citavi file from jablib/src/test/resources/org/jabref/logic/importer/fileformat

• [x] I own the copyright of the code submitted and I license it under the MIT license
• [/] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [/] Tests created for changes (if applicable)
• [x] Manually tested changed features in running JabRef (always required)
• [x] Screenshots added in PR description (if change is visible to the user)
• [x] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [x] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

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[subhramit]

Also please restore the "How to test" section in the PR description

[Siedlerchr]

I'm fine with the change and all tests pass. the citativ tasks Needs to be removed from the gradle scripts now as well

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[calixtus]

I am not sure if this code is more readable and maintainable than the old one.

imho it is. it reduces complexity a lot by easing the build tasks and reducing magic mappings.

please introduce string constants to replace the magic strings, then we can merge.

[trag-bot[bot]]

@trag-bot didn't find any issues in the code! ✅✨