fix(data-classes): keep CaseInsensitiveDict on copy and merge

[chiruu12]

Issue number: closes #8536

Summary

Changes

CaseInsensitiveDict now overrides copy, __or__, __ror__ and __ior__. copy, | and the reflected | return a CaseInsensitiveDict, and all of them go through the existing update, so new keys are lowercased the same way as everywhere else.

Two tests added to tests/unit/data_classes/required_dependencies/test_common.py. Both fail on develop and pass with the change.

User experience

Before, event.headers.copy().get("Content-Type") returned None, headers | {...} gave back a plain dict, and headers |= {"X-Trace-Id": "1"} stored X-Trace-Id without lowercasing it.

After, a copy or merge of event.headers keeps case-insensitive lookup.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Disclaimer: We value your time and bandwidth. As such, any pull requests created on non-triaged issues might not be successful.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.92%. Comparing base (5524980) to head (661bf96).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8537   +/-   ##
========================================
  Coverage    96.91%   96.92%           
========================================
  Files          317      317           
  Lines        15959    15976   +17     
  Branches      1411     1413    +2     
========================================
+ Hits         15467    15484   +17     
  Misses         349      349           
  Partials       143      143           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud