Fixes three output-fidelity bugs in pubmed_format_citations surfaced
by field-testing against real PubMed records:
• APA: trailing period before (Year) for collective authors
(ATLAS Collaboration, KEYNOTE-024 Investigators, ACTT-1, …)
• RIS: expand PubMed truncated page ranges (737-8 → 737/738)
• BibTeX: strip trailing period from title before emission
Spec deviations also corrected:
• MLA p./pp. branching per MLA 9 §6.56
• RIS abstract whitespace normalization (structured abstracts)
• getYear falls back to articleDates before yielding n.d.
Data surfaced that was previously dropped on the floor:
• publicationTypes → BibTeX entry type / RIS TY code
• RIS SN (ISSN, with eISSN fallback); BibTeX issn
• PMC URL (second RIS UR) + BibTeX pmcid when pmcId present
• MeSH descriptor names merged into RIS KW / BibTeX keywords (dedup)
Adds 11 new test cases. Full formatter suite (25/25) passing.