test: use e2e utils in tests that change epoch

[snormore]

This PR updates tests that change epochs (mostly in app) to use the e2e test utils, so that the node is started and most components are included. This is in prep for the committee beacon component, which will need to be up and running for epoch change to progress. After this, the tests will just work without more updates to them when the new component is added.

A few things are included to support this:

• Add TransactionClient to core/utils that helps with submitting and executing transactions, and waiting for them to complete or revert. This is used only in tests here, but is in core/utils because it will also be used in the committee beacon component for submitting transactions.
• Add poll_util helper to core/utils that's used in the e2e test utils, directly in tests, and in the transaction client.
• Update signer and notifier to wait for genesis on start; in support of the e2e test utils which start nodes without genesis, discover their random ports, then build and apply genesis from there.