[cuco][cudax] Enable map benchmarks with arbitrary key/value sizes

cuco's map benchmarks currently have the restriction type combinations with `sizeof(Key) != sizeof(Value)` are skipped during the benchmark run. The anecdotal reason for this was to cut down on overall benchmark runtime.

The problem is that users may want to benchmark a certain type combination that is then automatically filtered out by through the applied constraint.
We may want to find a better mechanism for this.

Start by locating cuco's map benchmark definitions and the constraint that skips key/value combinations with different sizes. Trace how the constraint is applied during the benchmark run, then define a mechanism that allows selected arbitrary combinations without forcing every combination to run; done means those combinations execute when requested while runtime remains manageable.

Written by the indexing model from the issue text.