Support ++ for concat in classical DSL

[ausbin]

Option 1 of this convo: #22 (comment)

Acceptance Criteria

1. x ++ y is supported in the @classical DSL
2. Operator overloads exist on the bit type
3. Operator overloads tested in runtime unit tests
4. convert_ast unit tests test ++ syntax
5. Integration tests for example programs with ++ syntax