Added length unit conversions (#5373)

* Added length unit conversions

Conversion of length units were added with respective tests being implemented and passed.
Available Units:- Metre,Kilometre,Feet,Inch,Centimeter,Yard,Foot,Mile,Millimeter

* Formatted File

File was formatted to go as per repo rules

* Reformatted file

* Reformatted code once again

* Added more test 

Added test to evaluate whether the code handles wrong arguements passed

* Update length_conversions.py

* Update length_conversions.py

* Update length_conversions.py

* Update length_conversions.py

* Update length_conversions.py

* Update length_conversions.py

* Update length_conversions.py

* Fixed  Minor errors in test

One of the test was failing and it was fixed

Co-authored-by: Christian Clauss <[email protected]>