refactor(sequencer): refactor app

[ethanoroshiba]

Summary

Large refactoring of the sequencer app.

Background

The sequencer app had a lot of duplicated code due to methods which did similar things slightly differently. In addition to this, naming of these different methods was confusing, with some using the outdated begin_block and end_block ABCI methods, and others just being helper methods. This refactor is meant to make the sequencer app clearer in its design and eliminate duplicated code.

Changes

• Created AppAbci trait for housing all of the app's methods which correspond to ABCI methods.
• Combined app::begin_block and app::end_block with their corresponding calling methods.
• Removed begin_block and end_block from Component, since they were largely unimplemented. Moved all implementations of these to prepare_state_for_execution (formerly pre_execute_transactions) and update_state_and_end_block (formerly post_execute_transasctions).
• Renamed Component to Genesis to reflect its only remaining method, init_chain.
• Refactored execute_transactions_prepare_proposal and execute_transactions_process_proposal to utilize shared code, and renamed them prepare_proposal_tx_execution and process_proposal_tx_execution for clarity as to how they fit in with the ABCI methods.

Testing

Fixed all tests which depended upon this code, now all passing.

Changelogs

Ensure all relevant changelog files are updated as necessary. See
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categories. Replace this text with e.g. "Changelogs updated." or "No updates
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Related Issues

closes #1785

[ethanoroshiba]

After offline discussion, I am going to break this up into many smaller PRs.