feat(ci): split release fixture builds across multiple fork-range runners

[danceratopz]

🗒️ Description

STILL WIP, needs self-review

Split multi-fork fixture releases (stable, develop) across parallel runners by fork range, reducing release CI wall-clock time. Follows the same pattern established in #2529 for the py3 tox env.

How it works:

• Features in feature.yaml can now declare fork-ranges — a list of {label, from, until} entries that partition the fork range across runners.
• A new generate_build_matrix.py script reads the config and emits a flat build matrix (feature × fork-range) for GitHub Actions.
• Each split runner fills its fork range to a directory with --generate-all-formats, then a combine job merges the directories and creates the final tarball via create_release_tarball.py.
• Features without fork-ranges (e.g., benchmark) keep current single-runner behavior unchanged.

Workflow structure changes from:

features → build (matrix: feature) → release

to:

setup → build (matrix: feature × range) → combine (matrix: split features) → release

Pre-alloc groups are fork-scoped (a group cannot span multiple forks, though a fork may have many groups), so phase 1 runs independently per runner with no cross-runner coordination needed. Merging is conflict-free directory combination since fixture files live under fork subdirectories (for_cancun/, for_prague/, etc.).

Also bumps stable fork range to include Osaka (latest mainnet fork) and develop to include Amsterdam (current fork in development).

🔗 Related Issues or PRs

• chore(ci): enable ported static in py3 and split into 5 parallel fork-range runners #2529 — same pattern applied to py3 tox env.

✅ Checklist

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

  uvx tox -e 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 86.24%. Comparing base (51fc631) to head (526edd1).
⚠️ Report is 14 commits behind head on forks/amsterdam.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #2592      +/-   ##
===================================================
- Coverage            86.35%   86.24%   -0.12%     
===================================================
  Files                  599      599              
  Lines                36904    36984      +80     
  Branches              3771     3795      +24     
===================================================
+ Hits                 31868    31895      +27     
- Misses                4485     4525      +40     
- Partials               551      564      +13     

Flag	Coverage Δ
unittests	86.24% <ø> (-0.12%)	⬇️

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