Clean up beacon state cache after each beacon action

[apexearth]

Description

Cleans up cached beacon state files downloaded by the Talos beacon verification actions.

Beacon state SSZ files are large, and each verification run can fetch a unique slot into contracts/cache/state_*.ssz. On long-lived Talos runners, these files can accumulate until the runner runs out of disk space.

This PR updates the beacon verification actions to prune old cached beacon state files after a successful action run.

Changes

• Runs beacon state cache cleanup after successful verifyBalances and verifyDeposits actions.
• Deletes only ./cache/state_*.ssz files older than 1 day.
• Leaves newer beacon state files in place for retries/debugging.
• Avoids touching unrelated Hardhat cache files.

Verification

• Ran pnpm prettier:js
• Ran pnpm prettier:ts
• Ran pnpm lint:ts
• Ran pnpm exec eslint utils/beacon.js
• Added a focused local cleanup check confirming:
  • old beacon state files are deleted
  • fresh beacon state files are kept
  • unrelated cache files are kept

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.63%. Comparing base (d784378) to head (6466b1e).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2936   +/-   ##
=======================================
  Coverage   44.63%   44.63%           
=======================================
  Files         110      110           
  Lines        4920     4920           
  Branches     1362     1362           
=======================================
  Hits         2196     2196           
  Misses       2721     2721           
  Partials        3        3           

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