Entity BN - Update to use new models module

After https://github.com/bcgov/entity/issues/23124 is done, the new models module can now be used with all BE components. The idea is we want to reference the new models module now instead of the models in Legal API.

Need to handle:
- [ ] update requirements.txt to reference models module
- [ ] update code references to refer to new models module
- [ ] any other required updates
- [ ] fix unit tests

Start with requirements.txt and locate the backend code references to the Legal API models; inspect the new models module mentioned in issue 23124. Run the affected unit tests after updating references and use their results to identify required compatibility changes. Done means the requirements, code references, and unit tests all use the new module.

Written by the indexing model from the issue text.