Update license

This MR updates the license headers in most files to the latest version of the GPL-3.0-or-later header, and updates the copyright attribution and years for 2025.

changed milestone to %GWDataFind Client 2.0.0

added packaging label

requested review from @duncan.meacher

added 13 commits

• 14c7782a...36cf1edb - 11 commits from branch computing/gwdatafind:main
• 3be00549 - update license headers
• 1d980cf1 - update copyright years

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approved this merge request

mentioned in commit 9c161a55

merged