[tool] degrees_to_radians

[shaurya703]

Fixes #373

Adds the degrees_to_radians tool: converts an angle from degrees to radians using math.radians (radians = degrees × π/180).

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 degrees_to_radians "180" -> 3.141592653589793; invalid input returns an error string