refactor(tooling): recipe renames, shell completions, and tox migration stub

[danceratopz]

🗒️ Description

Follow-up to the just migration PR. Three improvements:

1. Rename recipes for CLI ergonomics — revisit names from first principles for shorter, consistent, hyphen-separated names. Aligns with repo labels (e.g., A-test-tests → test-tests).
2. Shell auto-completion — document just --completions setup for bash, zsh, and fish in CONTRIBUTING.md.
3. tox.ini migration stub — contributors running old tox -e py3 get a bold migration message with the equivalent just recipe and install link, then a non-zero exit to avoid masking real errors.

Recipe renames

Before	After	Why
ethereum-spec-lint	lint-spec	Shorter; lint-* groups all linters for tab-completion
markdownlint	lint-md	Shorter; lint-* groups all linters for tab-completion
actionlint	lint-actions	lint-* groups all linters for tab-completion
spec-docs	docs-spec	docs-* groups all doc recipes for tab-completion
fast-docs	docs-fast	docs-* groups all doc recipes for tab-completion
tests_pytest_py3	test-tests	Aligns with A-test-tests repo label and commit scope
tests_pytest_pypy3	test-tests-pypy	Follows above
tests_benchmark_pytest_py3	test-tests-bench	Groups with test-tests family
pypy3	fill-pypy	Mirrors fill; clarifies it's a fill variant
json_loader	json-loader	Normalize underscores to hyphens
benchmark-gas-values	bench-gas	Shorter; bench-* groups benchmarks
benchmark-fixed-opcode-cli	bench-opcode	Shorter; bench-* groups benchmarks
benchmark-fixed-opcode-config	bench-opcode-config	Shorter; bench-* groups benchmarks

Shell Completion Example

Tox Migration Stub Helper Example

Full Recipe List

🔗 Related Issues or PRs

Follow-up to the just migration PR:

• feat(ci,tooling): replace tox with just ethereum/execution-specs#2555

✅ Checklist

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

Cute Animal Picture

[SamWilsn]

I'd prefer we just hard break and remove tox.ini

This stub doesn't preserve backwards compatibility, and I think most people would check the readme when tox fails.

[danceratopz]

Understand the sentiment, the screenshot in the PR description wasn't very illustrative.

The aim was to be a temporary helper (for say 2 months) for users who want to quickly know how to map their old "tox env" to the new "recipe".

That, and a friendly reminder for people switching often between branches that haven't rebased to forks/amsterdam yet.

Does that change how you feel about this temp feature? "No" is fine 😆 but I think it helps the migration path.

[SamWilsn]

I don't feel strongly about it, I just tend to try to cut as much code as possible. It is a nice helper, no argument here

[danceratopz]

Ok, I'll leave it in. I created a reminder for the beginning of May to delete it ))