Backend 3: Upgrade Python 3.10 to 3.13

[camd]

Summary

• Upgrade Python from 3.10 to 3.13 across Docker images, CI, and tooling config
• Update base images from Debian Bullseye to Bookworm (required for Python 3.13)
• Fix compatibility issues: netcat → netcat-openbsd, ENV format in Dockerfile
• Remove Python 3.10 backport deps (backports-asyncio-runner, exceptiongroup, tomli) that are now in stdlib
• Add setuptools to dev requirements (removed from stdlib in Python 3.13)
• Remove pyqt5/pyqt5-qt5/pyqt5-sip from common.txt — no Python 3.13 wheels and unused by Treeherder (declared by mozdetect but only needed for GUI/plotting features)
• Upgrade zstandard 0.22.0 → 0.23.0 (0.22 fails to build on 3.13)
• Add deprecation warning filters for datetime.utcfromtimestamp()/utcnow() (deprecated in 3.12+, TODO to migrate to timezone-aware calls)

Dependencies

• Builds on Phase 2: Django 5.1 → 5.2 LTS

Known limitations

• mozdetect declares pyqt5 as a dependency, but PyQt5 has no Python 3.13 wheels. Since Treeherder only uses mozdetect's data analysis functions (not GUI), this is safe to skip. pip check in CI is filtered to allow this.
• datetime.utcfromtimestamp() and datetime.utcnow() calls are suppressed via warning filters rather than migrated — there are 20+ call sites across source and tests. A follow-up PR should migrate these to datetime.fromtimestamp(ts, datetime.UTC).

Test plan

• Full backend test suite passes (1360 passed, 2 skipped, 9 xfailed)
• Docker dev image builds and runs on Python 3.13
• pip check passes (with known mozdetect/pyqt5 filter)
• CI linters pass (tox -e linters)
• Verify production Docker image builds cleanly

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.55%. Comparing base (f746007) to head (2a8023a).

Additional details and impacted files

@@                          Coverage Diff                           @@
##           camd/back-end-package-upgrade-phase-2    #9321   +/-   ##
======================================================================
  Coverage                                  82.55%   82.55%           
======================================================================
  Files                                        616      616           
  Lines                                      35312    35312           
  Branches                                    3323     3313   -10     
======================================================================
+ Hits                                       29152    29153    +1     
+ Misses                                      5816     5815    -1     
  Partials                                     344      344           

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[gmierz]

Just want to make a note here that I've filed an issue in mozdetect to get rid of pyqt there, I checked and even with the new graphing capabilities, we don't need to have those to build the graph: gmierz/mozdetect#3