Tests electronics/electric_conductivity.py #9943 (#12437)

* Function conversion rectangular number to polar

* #9943 : adding test to elelectronics/electric_conductivity.py

* updating DIRECTORY.md

* Apply suggestions from code review

* updating DIRECTORY.md

* Rename rec_to_pol.py to rectangular_to_polar.py

* updating DIRECTORY.md

* Update conversions/rectangular_to_polar.py

* Update conversions/rectangular_to_polar.py

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Co-authored-by: Julia <julia.de-jesus-aragao@imt-atlantique.net>
Co-authored-by: juliaaragao <juliaaragao@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>
Co-authored-by: cclauss <cclauss@users.noreply.github.com>