Remove text unit grouping

[natoverse]

Removes the group_by_columns config that would group documents before chunking. In practice this is never used, but adds a lot of complexity to maintain.

[Copilot]

Pull Request Overview

This PR removes the group_by_columns configuration option from text chunking, simplifying the system by eliminating the ability to group documents before chunking. The change moves from a one-to-many or many-to-many relationship between documents and text units to a strict one-to-many relationship where each text unit belongs to exactly one document.

• Removes group_by_columns parameter from chunking configuration and related workflows
• Changes text unit data model from document_ids (list) to document_id (single string)
• Updates test files to reflect new chunking behavior and token counts

Reviewed Changes

Copilot reviewed 23 out of 32 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
graphrag/config/models/chunking_config.py	Removes group_by_columns field from ChunkingConfig
graphrag/data_model/text_unit.py	Changes document_ids to document_id in TextUnit model
graphrag/index/workflows/create_base_text_units.py	Simplifies chunking logic by removing document grouping
graphrag/index/workflows/create_final_*.py	Updates workflows to use document_id instead of document_ids
tests/verbs/test_*.py	Updates test assertions for new chunking behavior
docs/*.md	Updates documentation to reflect removal of grouping feature

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}