Converts a strict clock model to the `state` section of the XML as text
Arguments
- inference_model
a Bayesian phylogenetic inference model. An inference model is the complete model setup in which a site model, clock model, tree prior and more are specified. Use create_inference_model to create an inference model. Use check_inference_model to check if an inference model is valid. Use rename_inference_model_filenames to rename the files in an inference model.