Add cost analysis functionality

[verovaleros]

Description

Implemented a function that retrieves the number of messages to translate, calculates the number of total tokens, and then calculates the total cost of the translation based on the current pricing from Open AI.

For each message, we craft the request to be sent to OpenAI and calculate the tokens for that request. In this early implementation, we assume the output tokens will be the same as the input tokens.

The prices are taken from the OpenAI documentation at the time of writing this PR. TODO keywords are added to do a better implementation on the next iteration.

Fixes #11

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• The tool was tested locally with various parameters
• The tests passed locally

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings