Allows users to register a custom metric function so it can be used by name
within kerasnip model specifications.
register_keras_metric(name, metric_fn)No return value, called for side effects.
The name to register the metric under (character).
The metric function.
Registered metrics are stored in an internal environment. When a model is
compiled, kerasnip will first check this internal registry for a metric
matching the provided name before checking the keras3 package.
register_keras_optimizer(), register_keras_loss()