fix(tooling): include namespace packages in coverage reports

[danceratopz]

🗒️ Description

Enable coverage.py's include_namespace_packages option so that never-imported modules under the ethereum.forks namespace package count towards the coverage denominator (at 0%); this gives all coverage uploads the same denominator and explains the apparent coverage drop seen in #2975, where fill-only reports silently excluded the never-imported spurious_dragon and tangerine_whistle fork trees.

🔗 Related Issues or PRs

Related to #2975.

✅ Checklist

• All: Ran fast static checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  just static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.29%. Comparing base (5f132e7) to head (321d465).
⚠️ Report is 10 commits behind head on forks/amsterdam.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #2982      +/-   ##
===================================================
- Coverage            90.52%   81.29%   -9.24%     
===================================================
  Files                  535      620      +85     
  Lines                32893    36635    +3742     
  Branches              3021     3311     +290     
===================================================
+ Hits                 29778    29782       +4     
- Misses                2596     6335    +3739     
+ Partials               519      518       -1     

Flag	Coverage Δ
unittests	81.29% <ø> (-9.24%)	⬇️

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