Провести код ревью тестового задания, Spring Boot, REST API

Нужно убедиться что тестовое задание выполнено правильно, с ипользованием примеров из документации и паттернов

Requirements

You are free to choose any JVM language to complete the challenge in, but your application has to run in Maven.

The API has to be threadsafe with concurrent requests.

The solution has to work without a database (this also applies to in-memory databases).

Your service must not store all transactions in memory for all time. Transactions not necessary for correct calculation MUST be discarded.

Unit tests are mandatory.

mvn clean install and mvn clean integration-test must complete successfully.

Please ensure that no changes are made to the src/it folder.

In addition to passing the tests, the solution must be at a quality level that you would be comfortable enough to put in production.

Полные требования во вложении. Задание делать не нужно, оно уже сделано, нужно только провести код ревью