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 39.90%. Comparing base (ac79c82) to head (49d9010).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1281      +/-   ##
==========================================
+ Coverage   39.87%   39.90%   +0.03%     
==========================================
  Files         165      165              
  Lines       37747    37747              
  Branches     5865     5865              
==========================================
+ Hits        15052    15064      +12     
+ Misses      21597    21585      -12     
  Partials     1098     1098              

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