Rename dvc and zn modules

[PythonFZ]

Rename to:

class Node(zntrack.Node):
    outs_path: str = zntrack.outs_path()
    metrics_path: str = zntrack.metrics_path()
    plots_path: str = zntrack.plots_path()
    params_file: str = zntrack.params_path()

    outs: any = zntrack.outs()
    metrics: dict = zntrack.metrics()
    plots: pd.DataFrame = zntrack.plots()
    param: float = zntrack.params(1)

where each one, except params has cache: bool = True/False option.

[PythonFZ]

• fixed in Introduce new zntrack.<field> and zntrack.<field>_path #699