[CLUSTER] Fix scan command cursors & Fix scan_iter

[utkarshgupta137]

Pull Request check-list

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
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Description of change

Fixes #2003

[codecov-commenter]

Codecov Report

Merging #2054 (6e7f052) into master (878e2f2) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2054      +/-   ##
==========================================
+ Coverage   91.19%   91.21%   +0.01%     
==========================================
  Files         100      100              
  Lines       21248    21287      +39     
==========================================
+ Hits        19378    19416      +38     
- Misses       1870     1871       +1     

Impacted Files	Coverage Δ
redis/cluster.py	91.85% <100.00%> (+0.02%)	⬆️
redis/commands/cluster.py	93.47% <100.00%> (+0.79%)	⬆️
tests/test_cluster.py	97.41% <100.00%> (-0.10%)	⬇️
redis/asyncio/connection.py	82.75% <0.00%> (+0.11%)	⬆️

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[utkarshgupta137]

@chayim @dvora-h @Grokzen

[chayim]

@utkarshgupta137 This looks like a great fix. Let's see if we can get this into the 4.2.0 final release @dvora-h .