Refactor: rename module structure accordingly to ADR-009

[carbolymer]

Changelog

- description: |
    Refactor: change module structure according to [ADR-009](https://github.com/input-output-hk/cardano-node-wiki/wiki/ADR-009-cardano-api-exports-convention)
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
   - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
   - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

TODO

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff