fix(copyright): recover source comment action credits

[mstykow]

Summary

• Normalize bounded DCL and VOS comment prefixes before evaluating explicit author actions.
• Support date-qualified written by source-header credits.
• Recover comma-delimited action-credit sentences embedded in source lines while requiring a person-shaped name.
• Preserve those explicit attributions through the scanner guard for code-shaped spans.

Issues

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

Scope and exclusions

• Included: explicit action credits in source comments and code-adjacent comment sentences.
• Explicit exclusions: collective maintainer credits, handled in the next stacked layer.

How to verify

• Scan Perl 5.38.4 with --copyright; vms/myconfig.com, vos/compile_full_perl.cm, and cpan/Win32API-File/Makefile.PL should report Peter Prymmer, Paul Green, and Alexandr Ciornii respectively.
• Before/after corpus scans add exactly those three authors; Info-ZIP, musl, Dancer2, and Valgrind author output is unchanged, and copyright/holder output is unchanged across all five targets.

Intentional differences from Python

• None for the three motivating credits; the implementation is evidence-bounded rather than mirroring ScanCode internals.

Follow-up work

• Created or intentionally deferred: contactless collective maintainer credits and mixed author/copyright POD headings remain for the next stacked PR.

Expected-output fixture changes

• Files changed: none.
• Why the new expected output is correct: detector and scanner tests cover the new source-comment boundaries.

[mstykow]

@greptileai review