chore(sequencer): separate test utils from shared benchmark and test utils

[ethanoroshiba]

Summary

Separated utils only used by tests from utils used by both benchmarks and tests.

Background

This is to get rid of many strings of nested expects and allows mentioned in #1585

Changes

• Separated astria-sequencer::test_utils.rs into test_utils.rs and benchmark_and_test_utils.rs.
• Separated astria-sequencer::app::test_utils.rs into app::test_utils.rs and app::benchmark_and_test_utils.rs.
• Fixed all the imports which broke as a result.

Testing

All tests working

Related Issues

closes #1585