Update version to 6.6.3, Update copyright and Icepack

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Update version to 6.6.3, Update copyright and Icepack
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Ran quick_suite on derecho on 6 compilers, tests pass. Will do comprehensive testing before release.
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.

Update version from 6.6.2 to 6.6.3 in preparation for next release

Update Copyright to 2026

Remove trailing whitespace

Update Icepack to #2f31ee37f3a70, Icepack v1.5.3