Rerank 3.5 fixes

[billytrend-cohere]

This pull request introduces changes to the src/cohere/aws_client.py file, primarily focusing on the _event_hook function and the addition of a new function, get_api_version.

• The _event_hook function now extracts the api_version from the request URL's path, splitting it at the second-to-last slash. This version is then used to set the body["api_version"] when the endpoint is "rerank".
• A new function, get_api_version, has been added. It takes a version string as input and returns the corresponding integer version. The function uses a dictionary to map string versions to integers, with a default value of 1 for unknown versions.
• The get_endpoint_from_url function has been removed.