Add codesize index

[daniellehrner]

PR description

• Adds an optional code size to the flat db account
• Add a backfill scaffold to fill it in the background

Fixed Issue(s)

fixes #8762

Thanks for sending a pull request! Have you done the following?

• [ ] Checked out our contribution guidelines?
• [ ] Considered documentation and added the doc-change-required label to this PR if updates are required.
• [ ] Considered the changelog and included an update if required.
• [ ] For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• [x] spotless: ./gradlew spotlessApply
• [ ] unit tests: ./gradlew build
• [ ] acceptance tests: ./gradlew acceptanceTest
• [ ] integration tests: ./gradlew integrationTest
• [ ] reference tests: ./gradlew ethereum:referenceTests:referenceTests