feat(ci): optimize full test release workflow

[spencer-tb]

🗒️ Description

Note this is a WIP and a draft PR. Optimizes the full fixture release workflow by parallelizing fixture generation across forks. Instead of running separate stable and develop fills sequentially, we now:

• Phase 1: Generate all pre-allocation groups once --generate-pre-alloc-groups
• Phase 2: Fill fixtures for each fork in parallel (with multiple workers) using shared pre-alloc groups --use-pre-alloc-groups --fork=X
• Phase 3: Merge fork outputs into fixtures_stable.tar.gz and fixtures_develop.tar.gz

This reduces duplication since stable fixtures (Frontier -> Prague) are a subset of develop fixtures (Frontier -> BPO4).

Key Changes

Modifies the enginex pre-allocation fill flags:

• --generate-pre-alloc-groups now runs only Phase 1 (previously ran both phases).
• --use-pre-alloc-groups --generate-all-formats runs Phase 2 only with all fixture formats.
• Explicit phase flags take priority over --generate-all-formats.

Adds a new merge fixtures script, used at the end of the new release workflow:

• Merges per-fork fixture artifacts into combined tarballs
• Uses existing generate_fixtures_index() for proper index/hash generation
• Includes pre_alloc groups in output

Creates a new release_fixture_full.yaml workflow, stages below:

• configure: Determines fork lists dynamically from codebase
• generate-pre-alloc: Phase 1 job (single runner)
• fill-fork: Phase 2 matrix job (parallel per fork)
• merge-fixtures: Phase 3 job (merges into stable/develop)
• release: Creates GitHub release

Remaining Todos

• Validate update fill flags, add test cases here.
• Add tests for a limit on tests, to validate the Phase 1 to Phase 2 steps with a small subset of tests.
• Add tests for the Phase 2 to Phase 3 section when merging fixture runners, all these tests should run in CI.

🔗 Related Issues or PRs

N/A.

✅ 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 adding an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

Cute Animal Picture

[spencer-tb]

https://github.com/ethereum/execution-specs/actions/runs/20103055503

[spencer-tb]

Note this is just a concept for now. After chatting with @danceratopz we both came to the same conclusion seperately that we should have an index file, that splits tests to fill across runners. The suggestion is to use the pytest-split plugin to split tests by worker based on their fill duration. One issue with this approach is that we would lose the fixture file folder structure. TBC.