Automate schedule selection based on `foundry.toml`, `kontrol.toml` and defaults

Related: https://github.com/runtimeverification/kontrol/pull/800

1. At the moment, the default schedule is Shanghai, however, there're many projects using newer Solidity versions that cause an undefined instruction error in kontrol prove. Previously, we have postponed making Cancun the default schedule, however, we can do it now since we've implemented most of the EIPs; Cancun is also the default evm_version in Foundry.
2. To make the default schedule more obvious to users, we should also add the schedule = 'CANCUN' entry to the kontrol.toml file that gets generated by kontrol init.
3. Another way to set schedule/evm version is by providing the evm_version = 'cancun' field in foundry.toml. We should probably recognize that as well and decide on the priority between Kontrol's --schedule and foundry.toml's, evm_version (I'd suggest schedule > evm_version).

The issue names kontrol prove, kontrol init, foundry.toml, and the generated kontrol.toml; start by tracing how schedule and evm_version configuration is currently resolved. Check the related pull request for existing work, then verify the default, generated configuration, and precedence behavior described in the issue with focused tests or command runs.