feat: add rectangular to polar coordinate conversion

[AliAlimohammadi]

Description

This PR adds a rectangular (Cartesian) to polar coordinate conversion to the conversions module.

The implementation:

• Computes magnitude using $r = \sqrt{x^2 + y^2}$
• Computes angle using $\theta = \text{atan2}(y, x)$ and converts it to degrees
• Rounds both magnitude and angle to two decimal places
• Uses only the Rust standard library

Changes Made

• Added rectangular_to_polar.rs under src/conversions
• Registered the new module in src/conversions/mod.rs
• Included unit tests covering typical and edge-case inputs

Notes

• No external dependencies were introduced
• Code is formatted with cargo fmt
• All tests pass successfully

Reference

Polar Coordinate System

[AliAlimohammadi]

@siriak, this is ready to be merged.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.06%. Comparing base (4402903) to head (9930af9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1003      +/-   ##
==========================================
- Coverage   96.06%   96.06%   -0.01%     
==========================================
  Files         371      372       +1     
  Lines       25943    25963      +20     
==========================================
+ Hits        24922    24941      +19     
- Misses       1021     1022       +1     

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