Add recursive function definitions to subsolver in sygus (#6824)

Add recursive function definitions to subsolver in sygus (#6824)

This passes recursive function definitions to the verification subsolver in sygus, with a default bounded limit of 3. This required improving the interface for setting up subsolvers by allowing custom options; the sygus solver statically computes an instance of the options that it uses in all calls.

This allows us to solve non-PBE sygus problems with recursive function definitions. The PR adds an example.