feat(spec-tool): enforce @final on leaf dataclasses

[danceratopz]

🗒️ Description

Follow-up to #2934. Add a FinalDecoratorHygiene rule to ethereum-spec-lint that enforces @final on leaf dataclasses across the specification.

PR #2934 added @final to leaf dataclasses (@dataclass and @slotted_freezable classes that are never subclassed) so mypyc can bypass the vtable for method calls and property accessors. This rule keeps that coverage from drifting as new forks are copied forward or new dataclasses are added.

The rule:

• Flags any leaf dataclass that is missing @final. Classes that are subclassed are skipped because they are not leaves, as are non-dataclass types such as enums, protocols, exceptions, and constant namespaces.
• Scans the whole specification once: every fork's modules plus the shared modules such as ethereum.state and ethereum.trace, including each package's __init__.py.
• Is registered in vulture_whitelist.py, since lints are discovered dynamically.

Note: Because the check is a whole-specification invariant, it runs once at the first fork position, so diagnostics are grouped under the earliest fork's header (frontier). Each message names the full module path, for example ethereum.forks.amsterdam.state_tracker, so the location is unambiguous.

Example output:

🔗 Related Issues or PRs

Related to #2934.

✅ 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 90.50%. Comparing base (9c2813e) to head (417f48b).

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #2965      +/-   ##
===================================================
+ Coverage            90.06%   90.50%   +0.43%     
===================================================
  Files                  488      535      +47     
  Lines                29562    32700    +3138     
  Branches              2686     3011     +325     
===================================================
+ Hits                 26626    29595    +2969     
- Misses                2457     2588     +131     
- Partials               479      517      +38     

Flag	Coverage Δ
unittests	90.50% <ø> (+0.43%)	⬆️

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[SamWilsn]

Good idea!