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.

debian/copyright

@@ -4,14 +4,14 @@ Upstream-Contact: Duncan Macleod <duncan.macleod@ligo.org>
 Source: https://git.ligo.org/lscsoft/gwdatafind
 
 Files: *
-Copyright: 2018-2022 Cardiff University
+Copyright: 2018-2025 Cardiff University
 License: GPL-3+
- This program is free software: you can redistribute it and/or modify
+ GWDataFind is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.
  .
- This package is distributed in the hope that it will be useful,
+ GWDataFind is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.