Access parametrization ids

[cazier]

This PR adds a new attribute to the Callspec2 class to provide the ID associated with a particular set of parametrizations.

We are using the parametrization data in a report generation tool we use, and accessing the IDs (particularly when it's either defined as the ids=[<parametrization names>] or ids=<parametrization function>) is not trivial as is.

Some tests are added to demonstrate the feature, particularly with different object types used in the parametrizations.