Improve annotation loading procedure in `s1_reader.burst_from_xml`

[seongsujeong]

Checked for duplicates

Yes - I've already checked

Alternatives considered

Yes - and alternatives don't suffice

Related problems

s1_reader.burst_from_xml() includes annotation reader. The logic can be improved by applying the comment below:

(#62 (comment))

Describe the feature request

I need the logic for annotation reader to take in zipfile object, rather than xml tree, so that the s1_reader.burst_from_xml() can be less populated.