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

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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 39.89%. Comparing base (6e71bc5) to head (a96afe0).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1281      +/-   ##
==========================================
+ Coverage   39.05%   39.89%   +0.84%     
==========================================
  Files         165      165              
  Lines       37745    37747       +2     
  Branches     5864     5865       +1     
==========================================
+ Hits        14740    15060     +320     
+ Misses      21879    21587     -292     
+ Partials     1126     1100      -26     

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