propagate flags too restrictive

1. It proofs a little unwieldy and contraintuitive that propagateFlags should only work on the last columns flags. (also strange things happen on data that results from align application)

• could be lifted with an additional keyword allowing for targeting columns with e certain label

2. The implementation only allows for application with regularily sampled data.

• can easily be lifted with wrapping pandas.reindex

Added the following advanced propagateFlags implementation for a use case and see no reason not to add that to the stat would add it to base library.

def _propagateTrue(flagser,
                   method,
                   tolerance):
    """
    Helper function.
    Propagates True entries in boolean Series by `tolerance` in direction indicated by `method`
    """
    f = flagser[flagser]
    return f.reindex(flagser.index, method=method, tolerance=tolerance, fill_value=False)

@flagging()
def propagateFlagged(qc: saqc.SaQC,
                   field: str | list[str],
                   method: Literal["ffill", "bfill"],
                   window: str,
                   prop_label: str = None,
                   **kwargs):
    """
    qc: SaQC object
    method: direction of propagation ("ffill": forward, "bfill": backward)
    window: extent of flags propagation (given as Offset String)
    prop_label: label of flag to propagate (if none is given, the result from isflagged(field) will be propagated instead)
    """

    prop_func = functools.partial(_propagateTrue, method=method, tolerance=window)
    f = lambda x: prop_func(isflagged(x, prop_label))
    return qc.flagGeneric(field, func=f, **kwargs)