Make SMT timeout increase strategy configurable

[geo2a]

In a recent PR, we have changed the SMT retries logic in Kore to scale the timeout exponentially.

When combined with the work to empower the simplifications Booster by using the SMT solver there as well, this leads to very long queries that still result in Unknown in Kore.

In order to have finer control, we need to introduce a command-line option that would allow to configure the scaling strategy:

• --smt-timeout-scaling linear will use the factors 2, 3, 4, ...
• --smt-timeout-scaling exp will use the factors 2, 4, 8, ...