How to hint users about Python packages' depending on specific versions of dependencies?

As the Python ecosystem assumes propagated dependencies, Python packages in Nixpkgs should not specify a specific version of the dependent package (e.g., pydantic instead of pydantic_1 or django instead of django_5). Packagers could workaround the version constraints with pythonRelaxDeps.

However, some Python packages rely on specific major versions of dependencies to function. How do we make such constraints discoverable to package users?