This derives truncation functions for ByDepthDesign and BenchmarkingDesign
such that paired list information (depths, circuits, idealouts)
are maintained through truncation.

Allows optional return of number of native gates
per Clifford during random circuit compilation,
and stores these in the CliffordRBDesign.
Adds utility function for computing average native gates per Clifford,
and ensures this works through design truncation.
Also adds a missing utility to compute total number of gates to Circuits.

Generalizes serialization/truncation for attributes
that are "paired" with the circuit lists in BenchmarkingDesigns.
This removes the code duplication in inherited classes
with more "paired" attributes,
such as CliffordRBDesign (with the new native gate info) and
BinaryRBDesign (with measurements/signs).

Adds an option `exact_compilation_key` that allows
the user to specify one of the CompilationRules to use for
deterministic Clifford compilation in CliffordRBDesign generation.