Fix IndexError, input validation, and enhance Converting_Roman_to_Integer

[Prayas340]

Description

The Converting_Roman_to_Integer script has several usability bugs, unhandled exceptions, and missing features:

1. Unhandled IndexError: Running python Converting_Roman_to_Integer.py with no CLI arguments throws an unhandled IndexError: list index out of range on sys.argv[1].
2. Case Sensitivity & Whitespace Failures: Providing lowercase Roman numerals (xiv) or inputs with whitespace causes unhandled KeyError crashes.
3. No Syntax / Character Validation: Non-Roman characters (ABC, 123) or invalid combinations (IIII, VV, IC) result in crashes or invalid numbers without informative error messages.
4. Shadowing Built-in Identifier: The script defines dict = {...}, shadowing Python's built-in dict type.
5. No Modular Structure: Logic is placed at module top-level without reusable functions or if __name__ == '__main__': guards.
6. Incomplete README: README.md is minimal (3 lines) and does not adhere to README_TEMPLATE.md.

Type of issue

• Bug
• Documentation
• Feature (Enhanced Script / Unit Tests)

Checklist:

• I have read the project guidelines.

• I have checked previous issues to avoid duplicates.

• This issue will be meaningful for the project.

• I have added steps to reproduce the bug:

  1. Run python Converting_Roman_to_Integer/Converting_Roman_to_Integer.py without arguments -> Crashes with IndexError.
  2. Run python Converting_Roman_to_Integer/Converting_Roman_to_Integer.py xiv -> Crashes with KeyError.
  3. Run python Converting_Roman_to_Integer/Converting_Roman_to_Integer.py IIII -> Incorrectly prints 4 without validation error.

• I have proposed a possible solution for the bug:

  • Add input sanitization (.strip().upper()) and regex syntax validation.
  • Support both CLI arguments and interactive fallback prompt.
  • Implement reusable functions roman_to_int(roman) and int_to_roman(num).
  • Add a comprehensive unit test suite and update README.md.