Add BLS key check to local testing workflow

[RonTuretzky]

Background

The integration tests have been updated to include a check for valid BLS keys. This change ensures that the local testing workflow also performs this validation.

Changes

• Modified .github/workflows/local-test.yml:
  • Added a new job step titled "Verify BLS key files".
  • This step iterates through testacc1.private.bls.key.json, testacc2.private.bls.key.json, and testacc3.private.bls.key.json in the .nodes/operator_keys/ directory.
  • It checks for the existence of each file.
  • It uses jq to extract the privateKey value and verifies its length. A length less than 70 characters is considered an error, as BLS keys on the BN254 curve are expected to be around 77 digits.
  • The workflow will exit with an error code if any key file is missing or if a private key is too short.
  • The workflow trigger has been updated to include the test-before-deprecation branch.

Testing

• Ensure the local testing workflow runs successfully with the new BLS key verification step.
• Manually inspect the output to confirm correct key file detection and length validation.