[tool] radians_to_degrees

[shaurya703]

Fixes #374

Adds the radians_to_degrees tool: converts an angle from radians to degrees using math.degrees (degrees = radians × 180/π), rounded to 4 decimal places to match the requested example.

Checklist

• File is in tools/ directory
• File has header comments (# tool, # description, # author, # example)
• File has a single run(*args) -> str function
• Stdlib only, no external dependencies
• Tested locally: python bitbox.py radians_to_degrees "3.14159" -> 179.9998; invalid input returns an error string