Remove 24 functions/methods with zero production callers, including
helpers only exercised by tests. Delete the standalone pickle_legacy
module. Adapt affected tests to use production equivalents or inline
constructions. 569 tests pass.
Normalize all Python sources to the standard ADN copyright block with
complete GPLv3 notice. Add legacy attribution on routing and dmr_utils
ports; drop SemVer wording from changelog and fix an unused test import.
Rodrigo Pérez