fix(copyright): recover source header author credits

[mstykow]

Summary

• recover contact-backed Original by and artifact-header credits such as hints by
• join bounded ... by: and wrapped action-attribution headers without absorbing following prose
• preserve multiple chained attributions on one source-header line

Issues

• Covers: False-positives when comparing provenant with scancode-toolkit output #1391

Scope and exclusions

• Included: generic, contact-backed source-header attribution forms and their continuation boundaries
• Explicit exclusions: unconstrained prose by phrases and ScanCode-only render differences

How to verify

• Scan Perl 5.38.4 with --copyright: Kaveh Ghazi, Andy Dougherty, Neil Bowers, and Luther Huffman are newly recovered; David Romano is upgraded to include the declared contact.
• Scan InfoZIP 3.0 with --copyright: author, copyright, and holder output is unchanged.

Intentional differences from Python

• ScanCode output is evidence, not the target contract. This keeps Provenant's cleaner existing renderings and rejects ScanCode false positives while recovering source-backed identities ScanCode itself misses, including Luther Huffman.

Expected-output fixture changes

• Files changed: testdata/copyright-golden/copyrights/misco4/linux-copyrights/net/dccp/ccids/lib/packet_history.c.yml
• Why the new expected output is correct: the fixture explicitly says the DCCP stack changes were written by Arnaldo Carvalho de Melo; the bounded wrapped-attribution logic now recovers that author.

[mstykow]

@greptileai review