Report structured metadata from CITATION.cff files

[andrew]

CITATION.cff currently contributes only a file path to the report. Use github.com/git-pkgs/citation to add structured authors, release details, identifiers, and preferred citations under resources.citation, while preserving resources.metadata.citation.

Human and Markdown reports include a bounded citation summary, with more metadata in verbose output. Parsing and validation have separate statuses so invalid or older files can retain useful metadata. Read errors, malformed YAML, and parser limits produce diagnostics without failing the scan. Citation metadata also follows changed-file filtering in brief diff.

Example output from brief --human testdata/citation-project:

Metadata:    CITATION.cff
Citation:      Example Research Software
Authors:       Alex van Example III, Research Team
Release:       1.20 2024-02-29
DOI:           10.1234/software
Identifier:    doi 10.1234/archive Archived releases
Cite:          The accompanying paper
Preferred DOI: 10.1234/paper
CFF:           1.2.0 valid

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