Improve public mul and div for AST

[LaRiffle]

Description

This is a small cleaning PR

Affected Dependencies

None

How has this been tested?

• Describe the tests that you ran to verify your changes.
• Provide instructions so we can reproduce.
• List any relevant details for your test configuration.

Checklist

• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests

[codecov]

Codecov Report

Merging #3835 into master will increase coverage by 0.06%.
The diff coverage is 95.31%.

@@            Coverage Diff             @@
##           master    #3835      +/-   ##
==========================================
+ Coverage   95.07%   95.14%   +0.06%     
==========================================
  Files         186      186              
  Lines       18857    18911      +54     
==========================================
+ Hits        17928    17992      +64     
+ Misses        929      919      -10     

Impacted Files	Coverage Δ
...orks/torch/tensors/interpreters/additive_shared.py	93.02% <88.00%> (-0.42%)	⬇️
...frameworks/torch/tensors/interpreters/precision.py	97.53% <100.00%> (+0.27%)	⬆️
test/torch/tensors/test_additive_shared.py	100.00% <100.00%> (ø)
syft/messaging/message.py	92.69% <0.00%> (-0.20%)	⬇️
syft/generic/pointers/object_pointer.py	82.08% <0.00%> (-0.14%)	⬇️
...frameworks/torch/tensors/interpreters/gradients.py	94.19% <0.00%> (-0.04%)	⬇️
test/generic/test_gc.py	100.00% <0.00%> (ø)
test/execution/test_translation.py	100.00% <0.00%> (ø)
syft/execution/plan.py	94.85% <0.00%> (+0.01%)	⬆️
syft/workers/message_handler.py	91.71% <0.00%> (+0.04%)	⬆️
... and 5 more

[gmuraru]

I look quickly, but LGTM!

[youben11]

LGTM! But I'm wondering, do we have to always get a remote tensor to compare with zero? Can't we do that remotely without fetching it?

[LaRiffle]

LGTM! But I'm wondering, do we have to always get a remote tensor to compare with zero? Can't we do that remotely without fetching it

Yeah indeed that could be a security issue. We could have a remote is_zero ? Like we have a is_none I think