Update tests to use contracts-bedrock safe-tools and stdStorage library

[prat-gpt]

For tests maintainability and readability use stdStorage library to get slots and lib/optimism/packages/contracts-bedrock/test/safe-tools/SafeTestTools.sol to generate multiple addresses with priv keys. Ref1, Ref2.

[mds1]

We should change _buildStarted back to a boolean as part of this: https://github.com/ethereum-optimism/superchain-ops/pull/640#discussion_r1965805909

[blmalone]

Closing as getBuildStarted is implemented and stdStorage is being used.