Implimented arXivId Parsing for PDF with arXivId

[ar-rana]

Used the 'parse' method in ArXivIdentifier to get arXivId and added a testcase for the same using the link give in the issue.
Closes #12000
Closes https://github.com/koppor/jabref/issues/47".

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[github-actions]

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[ar-rana]

@koppor could you please review this PR and suggest changes where I am wrong.

[Siedlerchr]

Thanks for your contribution. Please fix the check style issues first

[github-actions]

Your code currently does not meet JabRef's code guidelines.
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[ar-rana]

Hello maintainers, could you please review this PR, I have fixed the previous issues.
The extra changes that are being reflected are because I merged the latest changes from upstream, please ignore them they will not be there in the actual PR.

[Siedlerchr]

Codewise looks good to me. You have accidentally commited the csl styles submodules, see https://devdocs.jabref.org/code-howtos/faq.html#the-problem for a solution

[InAnYan]

Hmm, I tried to import these papers:

https://arxiv.org/abs/2406.14319
https://arxiv.org/abs/2412.06769

But JabRef didn't import it properly, and arXiv was null all the time

[ar-rana]

I have changed the getArXivId method to this in my local branch:

private String getArXivId(String arXivId) {
        if (arXivId == null) {
            arXivId = ArXivIdentifier.parse(curString).map(ArXivIdentifier::asString).orElse(null);
            if (arXivId != null) {
                if (curString.length() > arXivId.length() + 7) {
                    curString = curString.substring(arXivId.length() + 7);
                    extractYear();
                }
                return arXivId;
            }
        }
        return arXivId;
    }

and modified the ArXivIdentifier.parse method a little by altering the identifier to this String identifier = value.split(" ")[0]; at line 41.

this fixes the null arXiv problem that @InAnYan was encontering when externally importing the papers, but for some reason it still does not import the titles correctly except for the paper that was mentioned in the issue.

[github-actions]

JUnit tests are failing. In the area "Some checks were not successful", locate "Tests / Unit tests (pull_request)" and click on "Details". This brings you to the test output.

You can then run these tests in IntelliJ to reproduce the failing tests locally. We offer a quick test running howto in the section Final build system checks in our setup guide.

[InAnYan]

Hi, ar-rana! Thanks for working on this PR!

As holidays come soon, maintainers could be too busy these weeks, so don't worry if we give feedback too late

[Siedlerchr]

This could lead to a null pointer if there is no whitespace and you access the index

[ar-rana]

Hello Siedlerchr, I tested this method with empty/non-empty strings with/without whitespaces and it would only give a null pointer if the curString is null which does not seem to be the case here. So should I add a change here or leave it, as getDoi also work the same way