Non-synthesizable APIs on LogicStructure rely on packed

[mkorbel1]

Describe the bug

Non-synthesizable APIs such as posedge or value depend on the result of packed to compute their value. This is generally accurate, but has two major downsides:

• Calling packed creates and connects a new signal. If a testbench calls packed (directly or indirectly) on a signal within a Module, it will generate some additional hardware (though it won't have any functional impact).
• The previousValue will be null the first time it is called since packed is lazily initialized. This can cause surprising testbench failures.

To Reproduce

Call previousValue on a LogicStructure and observe that it is null.

Expected behavior

The APIs should not have side effects of creating hardware (even without functional impact) and should be functional in the same way as Logic.

Actual behavior

No response

Additional: Dart SDK info

No response

Additional: pubspec.yaml

No response

Additional: Context

No response