(retriever) Ensure batched OCR inference

[charlesbluca]

• Breakdown local OCR pipeline to enable batched inference
• Ensure that upstream stages effectively saturate OCR

Description

• Refactors local OCR to circumvent pipeline API that only accepts single-image inputs
• Refactors ocr_page_elements upstream stage to aggregate OCR inputs before sending to local model to ensure saturation

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• If adjusting docker-compose.yaml environment variables have you ensured those are mimicked in the Helm values.yaml file.