ENGDESK-39615: Add active_calls method to Connection class

[ai-swe-agent]

Description

This PR adds the active_calls method to the Connection class in the Telnyx Python SDK. This method allows users to retrieve active calls for a given connection.

Changes

• Added the nested_resource_class_methods decorator to the Connection class with the "active_call" resource and "list" operation
• Implemented the active_calls instance method that calls the generated list_active_calls class method
• Added tests for both the instance method and class method

Related Issues

Fixes: ENGDESK-39615

Usage

After this change, users will be able to retrieve active calls using either:

# Instance method
connection = telnyx.Connection.retrieve("connection_id")
active_calls = connection.active_calls()

# Class method
active_calls = telnyx.Connection.list_active_calls("connection_id")

[dmmc12]

Thanks for the catch on the other connection types @ADandyGuyInSpace. Any reason the CI's are failing right now and when can we merge?

[dmmc12]

@ADandyGuyInSpace friendly reminder to merge and push.