Improve code quality for currency formatting functions #574

Description

The format_currency and convert_real_to_text functions in currency.py need code quality improvements to meet current standards.

Functions to Update

• format_currency()
• convert_real_to_text()

Required Changes

• Update type hints to use modern Python typing conventions
• Fix and standardize docstrings (ensure proper format, parameters, return values, and examples)
• Review function signatures for consistency
• Add missing type annotations where needed

Acceptance Criteria

• All functions have proper type hints
• Docstrings follow project standards and include:
  • Clear description
  • Parameters with types
  • Return value description
  • Usage examples (if applicable)
• Code passes type checking
• Functions maintain backward compatibility