Ensure that all errors are created as pointers & fix TimeoutError's string representation

Some errors are not created as pointers. Ensure that all of them are consistent. TimeoutError's Error() method does not always result in a useful string representation because while Error() is a value receiver, even though it uses UnmarshalJSON() internally it can't call our custom marshalling method which is implemented as a pointer receiver

As a part of this we should check if other SDKs are using the short identifiers in timeouts and probably replace them with full identifiers.