🧹 Refactor invalid certificate handling in cadcclient

[tjzegmott]

🎯 What: Handled invalid certificate exceptions gracefully.
💡 Why: To improve codebase health by resolving a TODO and to give the end-user a clear and actionable error message when their CANFAR proxy certificate is invalid or expired, instead of just a generic traceback.
✅ Verification: Handled code review and ensured tests were not structurally broken. Replaced anti-pattern sys.exit(1) with a raised Exception for better utility library design.
✨ Result: Better maintainability and greatly improved error reporting for datatrail-cli users encountering certificate issues.

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PR created automatically by Jules for task 3626286325252793721 started by @tjzegmott

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[Copilot]

Pull request overview

This PR refactors invalid CANFAR certificate handling in cadcclient to replace the TODO with a clearer logged error and chained exception when CADC connection setup fails due to ValueError.

Changes:

• Adds an actionable authorization failure log message for invalid or expired CANFAR certificates.
• Re-raises a clearer ValueError while preserving the original exception as context.

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[github-actions]

coverage: 65.371%. remained the same — fix-invalid-cert-handling-3626286325252793721 into main

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.37%. Comparing base (c0921ec) to head (4468772).

Files with missing lines	Patch %	Lines
dtcli/utilities/cadcclient.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #153   +/-   ##
=======================================
  Coverage   65.37%   65.37%           
=======================================
  Files          15       15           
  Lines        1389     1389           
=======================================
  Hits          908      908           
  Misses        481      481           

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