Waterfall

Enables clear, sequential chaining of service objects and blocks, with execution continuing only on success, as shown in the FetchUser example where commands are linked in a flow.

Uses `dam` to halt flows on errors, bypassing subsequent commands and triggering `on_dam` blocks for reporting, providing a clean separation of happy and unhappy paths.

Offers a `with_transaction` method to wrap flows in database transactions, ensuring automatic rollback when dammed, as demonstrated in the Rails setup example with ActiveRecord.

Includes `reverse_flow` methods to undo actions in previously executed services if a later step fails, complementing transaction-based rollback for non-database side effects.