Feature to store `WaveDumper` output in memory

### Motivation

Since ROHD has become a [DartPad-supported](https://github.com/intel/rohd/discussions/272) package, it might be worth considering playground limitations. Attempting to use `WaveDumper` results in an error because the ability to save files is not available.

### Desired solution

Add the ability to store the output of `WaveDumper` in memory. Further, the user can do, for example, `print` at will (as with the generated SystemVerilog code).

### Alternatives considered

_No response_

### Additional details

I understand that for large projects, large `vcd`s can be generated that can take up all the memory if they are not flushed to disk. But it is acceptable for small projects/examples.