feat(loader): implement markdown parsing in MathpixPDFReader

[eliasjudin]

Add functionality to properly handle PDF content:

• Add parse_markdown_text_to_tables method to separate tables and text
• Fix load_data implementation to properly process documents
• Fix lazy_load_data method
• Improve document metadata handling for tables and text sections

The loader now correctly processes PDFs through Mathpix API and converts content to proper Document objects.

Description

• Added functionality to properly parse and process PDF content in MathpixPDFReader:
  • Implemented parse_markdown_text_to_tables method to correctly separate tables and text sections
  • Fixed load_data implementation to process documents with proper metadata
  • Added lazy_load_data method for memory-efficient document loading
  • Improved document metadata handling for both tables and text sections
• The loader now correctly processes PDFs through Mathpix API and converts content to proper Document objects

Type of change

• New features (non-breaking change).
• Bug fix (non-breaking change).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).

Checklist

• I have performed a self-review of my code.
• I have added thorough tests if it is a core feature.
• There is a reference to the original bug report and related work.
• I have commented on my code, particularly in hard-to-understand areas.
• The feature is well documented.

[taprosoft]

@eliasjudin please check the failed CI and comments.

[eliasjudin]

need to resolve this issue

1 validation error for CiteEvidence
evidences
  Input should be a valid list [type=list_type, input_value='["Let $M$ be a multiplic...\in M$ and $x \\in X$"]', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/list_type
Got 0 cited docs

any suggestions?

[eliasjudin]

page numbering is incorrect, all items say from page 1

[eliasjudin]

need to resolve this issue

1 validation error for CiteEvidence
evidences
  Input should be a valid list [type=list_type, input_value='["Let $M$ be a multiplic...\in M$ and $x \\in X$"]', input_type=str]
    For further information visit https://errors.pydantic.dev/2.9/v/list_type
Got 0 cited docs

any suggestions?

fixed this by adding check if str in citation.py and then wrapping to list