feat: modular parser and formatter v0

[chloedia]

This PR is making Megaparse modular with the creation of multiple basic "Formatters" such as :

• Table Formatters : Repass over the identified tables to improve their rendering
• Structured Formatter: Use the structured outputs from Claude or GPT-4o to render the file in a specific json

BREAKING CHANGE:

• Unstructured Parser will return a MegaParse Document (not a string), which can be rendered simply using str(document)
• This resulted in a change in the test

SOLVE #3464