Apply PEP8 styling and improve code quality

[bugfloyd]

This PR addresses several code quality improvements and applies PEP8 styling standards. The changes include:

• Apply PEP8 styling standards and reformat the code:

  • Improve spacing and indentation
  • Split long lines into multiple lines

• Enhance variable names and definitions:

  • Resolve shadowed variable names
  • Convert unused method parameters to private variables
  • Fix instances of variables being referenced before assignment
  • Improve parameter documentation for better readability

• Remove duplicate code and streamline logic:

  • Create a new method add_chat_request_to_usage_tracker in the ChatGPTTelegramBot class to centralize usage tracking logic
  • Define a new method add_current_costs in the UsageTracker class to handle cost calculations in a more concise manner

[n3d1117]

Thank you @bugfloyd 🚀