Add GROBID baseline comparison to benchmark workflow

[de-code]

part of https://github.com/eLifePathways/ScienceBeam2.0/issues/73

Inline GROBID prediction generation into benchmark.yml (conditional on predictions being absent), score baseline predictions via a new --split override in score.py, and produce a side-by-side comparison report. Adds variant field to eval.yml corpus config and baselines section declaring GROBID 0.9.0-crf as the reference tool.

[github-actions]

ScienceBeam Parser Evaluation

biorxiv

grobid 0.9.0-crf: 10 docs | sciencebeam-parser:main-f87246c2-20260526.2020: 9 docs | sciencebeam-parser:pr-613-3c18e6c0-20260527.1023: 9 docs

Field (method)	Type	grobid 0.9.0-crf	sciencebeam-parser:main-f87246c2-20260526.2020	sciencebeam-parser:pr-613-3c18e6c0-20260527.1023	Δ grobid 0.9.0-crf	Δ sciencebeam-parser:main-f87246c2-20260526.2020
title (exact)	string	0.889	0.941	0.941	+0.052	+0.000
title (levenshtein)	string	0.947	0.941	0.941	-0.006	+0.000
title (edit_sim)	string	0.939	0.944	0.944	+0.005	+0.000
abstract (levenshtein)	string	0.947	0.364	0.364	-0.584	+0.000
abstract (edit_sim)	string	0.947	0.541	0.541	-0.406	+0.000
author_full_names (levenshtein)	partial_ulist	0.970	0.962	0.962	-0.008	+0.000
author_full_names (edit_sim)	partial_ulist	0.933	0.926	0.926	-0.007	+0.000
affiliation_text (levenshtein)	partial_ulist	0.000	0.907	0.907	+0.907	+0.000
affiliation_text (edit_sim)	partial_ulist	0.000	0.891	0.891	+0.891	+0.000
keywords (levenshtein)	partial_ulist	0.901	0.000	0.000	-0.901	+0.000
keywords (edit_sim)	partial_ulist	0.907	0.000	0.000	-0.907	+0.000
body_section_titles (levenshtein)	partial_list	0.516	0.819	0.819	+0.303	+0.000
body_section_titles (edit_sim)	partial_list	0.472	0.764	0.764	+0.293	+0.000
acknowledgement (levenshtein)	string	0.750	0.875	0.875	+0.125	+0.000
acknowledgement (edit_sim)	string	0.726	0.871	0.871	+0.145	+0.000
first_reference_text (levenshtein)	string	0.000	0.875	0.875	+0.875	+0.000
first_reference_text (edit_sim)	string	0.000	0.870	0.870	+0.870	+0.000
reference_title (levenshtein)	partial_list	0.766	0.291	0.291	-0.475	+0.000
reference_title (edit_sim)	partial_list	0.727	0.343	0.343	-0.385	+0.000
reference_doi (levenshtein)	partial_ulist	0.954	0.860	0.860	-0.094	+0.000
reference_doi (edit_sim)	partial_ulist	0.871	0.775	0.775	-0.096	+0.000