ci: add mechanical formatting autofix workflow

[purusang]

Description

Adds a pull request workflow that applies deterministic mechanical formatting fixes and pushes them back to same-repository PR branches. The workflow currently runs Rust, TOML, and functional-test Python formatters:

• cargo fmt --all
• taplo fmt
• uv run ruff format in functional-tests

The existing lint workflows remain responsible for checking the resulting commit.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature/Enhancement (non-breaking change which adds functionality or enhances an existing one)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor
• New or updated tests
• Dependency Update

Notes to Reviewers

The workflow is limited to PR branches from this repository, so it does not try to push to fork PRs. It requests contents: write because the built-in GITHUB_TOKEN needs that permission to push formatter commits.

Is this PR addressing any specification, design doc or external reference document?

• Yes
• No

If yes, please add relevant links:

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added (where necessary) tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.
• I have disclosed my use of AI in the body of this PR.

Validation: actionlint .github/workflows/autofix-formatting.yml

AI assistance notice: This PR was prepared with AI assistance.

Related Issues

[github-actions]

Commit: 966f069

SP1 Execution Results

program	cycles	gas
EVM EE Chunk	824,732	969,394
EVM EE Account	404,056	498,593
Checkpoint	2,601,550	3,007,194

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.38%. Comparing base (b5d34b8) to head (e672c49).

@@            Coverage Diff             @@
##             main    #1937      +/-   ##
==========================================
- Coverage   84.42%   84.38%   -0.04%     
==========================================
  Files         637      637              
  Lines       76805    76805              
==========================================
- Hits        64840    64813      -27     
- Misses      11965    11992      +27     

Flag	Coverage Δ
functional	66.42% <ø> (-0.10%)	⬇️
unit	69.52% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 8 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[storopoli]

NACK.

2 things:

1. this adds a contents: write in permissions which is VERY VERY BAD for security purposes.
2. this also breaks the planned git commit signing requirement that we intend to roll before mainnet (see here).

A suggestion would be to add a contrib/git-hooks directory with a bunch of pre-commit hooks that would make impossible to do a commit that is not cargo fmted. Pair that up with a just recipe to install/uninstall the git hooks and voilà.