replace block generation delay with polling

[Oscar-Pepper]

Motivation

Chain index integration was held up by flaky and slow tests and increased failure rates due to underlying issues with test framework interacting with chain index. Fixing the test framework to use correct sleeping and to poll when generating blokcs instead of using fixed delays not only improves dev efficiency but fixes many failing tests in the chain integration (#596)

Solution

• remove OS sleeps
• replace fixed delays with polling
• return service subscriber in the test manager to reduce backend duplication and out-of-sync bugs

Tests

Specifications & References

Follow-up Work

PR Checklist

• The PR name is suitable for the release notes.
• The solution is tested.
• The documentation is up to date.

[dorianvp]

Some issues we're seeing here are highly related to #620, and #610.