Updating copyright header for 2026

[ksbeattie]

Fixes/Addresses:

Updates the copyright year range to include 2026 in the headers of nearly every file in the repo. Adds it to a few files that were missing it.

Summary/Motivation:

Changes proposed in this PR:

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the copyright and license terms described in the LICENSE.md file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.04%. Comparing base (bb11943) to head (e290c1c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1281      +/-   ##
==========================================
- Coverage   39.05%   39.04%   -0.02%     
==========================================
  Files         165      165              
  Lines       37745    37745              
  Branches     5864     5864              
==========================================
- Hits        14740    14736       -4     
- Misses      21879    21881       +2     
- Partials     1126     1128       +2     

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