Add a way to manage .pyi <-> .py consistency

### Body

We have quite a few cases where .pyi and .py files we have get desynchronized (for example:

* https://github.com/apache/airflow/issues/36224
* https://github.com/apache/airflow/pull/36406
* https://github.com/apache/airflow/pull/36405

We should find a way to keep them synchronized as changes are applied to either .py or .pyi

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.

Start by reviewing the desynchronization examples in issue 36224 and pull requests 36406 and 36405, then inspect the repository's existing handling of .py and .pyi files. Define how consistency should be maintained when either file changes and how it will be checked. Done means the project has an agreed mechanism that detects or prevents the reported mismatches.

Written by the indexing model from the issue text.