fix: single doc set in docarray

[davidbp]

Currently setting for example .text the attribute for a concrete Document in a DocumentArray results to setting the first character in the string.

# this works as expected in master
from docarray import Document, DocumentArray
da = DocumentArray([Document(),Document(), Document()])
da[[0,1],'text'] = ['jina','jana']
print(da[:,'text'])

# this does NOT work as expected in master
from docarray import Document, DocumentArray
da = DocumentArray([Document(),Document(), Document()])
da[[0],'text'] = 'jina'
print(da[:,'text'])

# this does NOT work as expected in master
import numpy as np
from docarray import Document, DocumentArray
da = DocumentArray([Document(),Document(), Document()])
da[[0],'id'] = '1234'
print(da[:,'id'])

In master

['jina', 'jana', '']
['j', '', '']
['1', 'b6ac7ce073ba11ecbdc7787b8ab3f5de', 'b6ac7d3073ba11ecbdc7787b8ab3f5de']

This happens because the setter has the sets the values in for _d, _vv in zip(_docs, _v) and when the input data is an iterable this is not probably what the user would expect

In this PR

['jina', 'jana', '']
['jina', '', '']
['1234', '92c2521e73ba11eca885787b8ab3f5de', '92c2526473ba11eca885787b8ab3f5de']

[codecov]

Codecov Report

Merging #42 (ae67c85) into main (699c041) will decrease coverage by 0.21%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   82.80%   82.58%   -0.22%     
==========================================
  Files          67       67              
  Lines        3193     3216      +23     
==========================================
+ Hits         2644     2656      +12     
- Misses        549      560      +11     

Flag	Coverage Δ
docarray	82.58% <66.66%> (-0.22%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
docarray/types.py	0.00% <0.00%> (ø)
docarray/array/document.py	86.97% <100.00%> (+0.11%)	⬆️
docarray/document/mixins/plot.py	69.56% <0.00%> (-23.30%)	⬇️
docarray/array/mixins/plot.py	60.89% <0.00%> (+0.09%)	⬆️
docarray/helper.py	65.58% <0.00%> (+1.29%)	⬆️

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[hanxiao]

will take this branch

[hanxiao]

good to go