feat: Add DocumentBlock support to LiteLLM integration

[pazevedo-hyland]

This PR adds support for DocumentBlock content in the LiteLLM integration, enabling users to send PDF and other document files to LLM providers through LiteLLM.

Changes Made

llm = LiteLLM(
    "litellm_proxy/bedrock-claude-3-7-sonnet-20250219-v1:0",
    api_base="...",
    api_key="sk-...",
)

document_block = DocumentBlock(
    data=pdf_data_in_bytes,
    document_mimetype="application/pdf",
    title="test_document.pdf",
)
text_block = TextBlock(text="Please analyze this document.")

message = ChatMessage(role=MessageRole.USER, content=[document_block, text_block])

# Send the message
chat_response = llm.chat([message])

New Features

• Added DocumentBlock support: Documents are now converted to LiteLLM expected format using type file with base64-encoded file_data.
• Enhanced test coverage: Added comprehensive tests for DocumentBlock conversion and integration.

Testing

• All existing tests pass
• New DocumentBlock tests added and passing
• Verified proper base64 encoding/decoding
• Confirmed LiteLLM format compatibility
• Tested with claude 3.7 sonnet via litellm proxy

[pazevedo-hyland]

@AstraBert take a look at this if possible

[AstraBert]

@pazevedo-hyland yep, taking a look at this tomorrow, thanks for the integration🙏

[pazevedo-hyland]

@AstraBert you have any clue why the imports are failing on unit tests?

[AstraBert]

Hey @pazevedo-hyland, it's a uv problem: the version of llama-index-core listed in uv.lock is 0.12.33.post1, which didn't have DocumentBlock in it. I'll take care of changing it, dw :)