[WIP] Implement QubitUnitary's decomposition under the new system

[astralcai]

Context:

Description of the Change:

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[sc-88371]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.64%. Comparing base (235f2c3) to head (baa1580).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7211   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files         513      515    +2     
  Lines       50172    50229   +57     
=======================================
+ Hits        49996    50053   +57     
  Misses        176      176           

☔ View full report in Codecov by Sentry.
📢 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.