- fold string literal comparisons
- fold non-decimal bit shifts
- fold non-decimal integer comparisons
- fold decimal bitwise AND and OR
- simplify cast expressions before elaboration
- remove duplicate cast expression traversal
- flatten concatenated numbers in a single pass

The implicit type of a localparam is not always needed. This improves
performance when complex localparam expressions are processed.

- event expressions use Expr over LHS
- stricter AST representation of event controls
- property specs use event expressions directly