Use bdde-multiarch to setup qemu for multiarch

[jeking3]

See jeking3/bdde#10 for details. I upgraded bdde to v3.1.0, and changed how qemu is configured. Sadly the multiarch/qemu-user-static project hasn't been updated since 2023. I reached out to one of the authors.

The job that matters here is the s390x big-endian one... it would be the only one affected by this change.

This will fix https://github.com/cppalliance/decimal/actions/runs/14069869895

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (605750a) to head (55d6dff).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #275   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines           22        22           
  Branches        12        12           
=========================================
  Hits            22        22           

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 605750a...55d6dff. Read the comment docs.

🚀 New features to boost your workflow:

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

[Flamefire]

Great, thanks!