ENH: Store Annotation data in consistent format

[sammlapp]

Is your feature request related to a problem? Please describe. I find it confusing that the base class for all annotations (Annotation) stores data in different ways for "sequence" and "bounding box" type annotations, since these fundamentally contain similar (overlapping) data types.

Describe the solution you'd like Annotation class could be refactored to store annotations in a dataframe with columns for time0, time1, freq0, freq1. It would contain methods or properties that allow the user to get either a list of bbox or a sequence/ list of sequences. This would enable all of the current functionality while storing data in a consistent format regardless of the source of the annotation.

class Annotation:
    def __init__(self,df,annotation_file,notated_file):
        self.df = df #columns time0, time1, freq0, freq1 etc
        self.annotation_file=annotation_file
        self.notated_file=notated_file
    
    @classmethod
    def from_bboxes(cls, bboxes,annotation_file,notated_file):
        ...
        return cls(df,annotation_file,notated_file)
    
    @classmethod
    def from_sequences(cls,sequences,annotation_file,notated_file):
        ...
        return cls(df,annotation_file,notated_file)

    @property
    def sequences(self):
        return self._make_sequences_from_df()

    def _make_sequences_from_df(self):
        ...
        return list_of_sequences

    @property
    def bboxes(self):
        return self._make_bboxes_from_df()

    def _make_bboxes_from_df(self):
        ...
        return list_of_bboxes

#example usage with sequences
anns = Annotation.from_sequences(sequences)
anns.sequences # gives list of sequences

#example usage with bboxes
anns = Annotation.from_bboxes(bboxes)
anns.bboxes # gives list of bboxes

Describe alternatives you've considered Alternatively to storing annotations as a dataframe, Annotation could store a list of BBox objects, and a sequences property could call a method _bbox_to_seq() to convert the list of BBox to a sequence.

Additional context This vocalpy thread contains discussion of this idea https://forum.vocalpy.org/t/use-of-both-sequence-and-bbox-in-annotation-class/63/6