Add article type filtering for PubMed format generation

[Copilot]

Problem

Previously, PubMed format was being generated for all articles regardless of their document type. However, according to NCBI PubMed documentation, PubMed only accepts specific types of articles for submission.

This was generating unnecessary PubMed XML files for ineligible article types such as book reviews, abstracts, news items, and other document types that PubMed does not accept.

Solution

This PR implements filtering logic to only generate PubMed format for eligible article types:

Eligible article types:

• research-article
• review-article
• case-report
• editorial
• letter
• brief-report
• rapid-communication
• reply
• article-commentary
• correction
• retraction
• addendum

Changes

1. article/choices.py: Added PUBMED_ARTICLE_TYPES constant containing the list of eligible article types based on NCBI guidelines

2. article/models.py: Modified ArticleFormat.generate_formats() to check the article type before generating PubMed format:

   # Only generate PubMed format for eligible article types
   if article.article_type in choices.PUBMED_ARTICLE_TYPES:
       cls.generate(
           user,
           article,
           "pubmed",
           article.sps_pkg_name + ".xml",
           pubmed.pipeline_pubmed,
           indexed_check=False,
       )

3. article/tests.py: Added comprehensive test suite (PubMedArticleTypeFilteringTest) with 4 test methods to verify:

   • PubMed format is generated for eligible article types
   • PubMed format is NOT generated for ineligible article types
   • Other formats (PMC, CrossRef) continue to work as expected

Impact

• Before: PubMed format generated for ALL articles
• After: PubMed format only generated for eligible article types
• Other formats (CrossRef, PMC) remain unaffected
• Reduces unnecessary processing and file generation
• Ensures compliance with PubMed submission guidelines

Fixes the requirement from issue: scieloorg/PC-Programs#3374

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Selecionar os artigos para a geração do formato PubMed</issue_title>
<issue_description>### Descrição da tarefa
Somente para os seguintes tipos de documentos:
https://www.ncbi.nlm.nih.gov/books/NBK3828/#publisherhelp.What_types_of_articles_are

demanda registrada inicialmente em: scieloorg/PC-Programs#3374</issue_description>

Comments on the Issue (you are @copilot in this section)

@robertatakenaka @scieloorg/scielo-ps-developers por favor, adicione aqui exemplos de xml pubmed compactados (zip) original e corrigido. Assim atenderemos este issue com mais precisão.

Fixes #1081

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