Due to the decorators used in the GUI code with lit which is not
supported natively by node the tests under helper.test.js return module
error. This commit fixes by refactoring the `simpleMetricFactory` method
to remove dependency on code using experimental decorators.
Fix the string conversion of the curveMetrics and push the formatting
logic to the consumer that require this (eg. WorkoutRecorder). This
enables other consumers of curveMetrics to use non-rounded, "raw" data
instead of preformatted as well as avoid potential future bugs from the
type conversion.
Abász