Soltest error handling refactor

[cameel]

Depends on #16013.

More refactors extracted from #16012, this time not purely cosmetic:

• Replaces throwing std::runtime_error with dedicated exception types.
  • Unlike runtime_error, the new types can be used with solThrow()/solRequire() because they inherit from util::Exception.
  • We can now easily distinguish them from unhandled exceptions caused by bugs and handle them more gracefully, by just printing the message, without all the debug info clutter. This makes the assembly parsing errors from evmasm test case #16012 much more readable.
• Prevents the infinite update loop when your custom test case does not add a newline at the end of expectations (a common mistake).
• Also, prints a hint when the expectations don't match but look identical, because the difference is only in whitespace.
• Tweaks a few messages and changes the output from stdout to stderr in some cases.