feat: add LiteParseLoader (LiteParse optional extra)

[jexp]

Summary

• Adds LiteParseLoader in a new neo4j_graphrag.experimental.components.liteparse_loader module as an alternative PDF/document loader backed by LiteParse — a local, zero-cloud Rust parser with optional Tesseract OCR support
• data_loader.py is unchanged — LiteParseLoader lives in its own module alongside the optional-dependency import guard
• New liteparse optional extra: pip install "neo4j-graphrag[liteparse]"
• Drop-in replacement for PdfLoader; pass as file_loader=LiteParseLoader() to SimpleKGPipeline

Changes

• src/neo4j_graphrag/experimental/components/liteparse_loader.py — new module with LiteParseLoader
• pyproject.toml — liteparse = ["liteparse>=2.0.0,<3.0.0"] optional extra + mypy override
• CHANGELOG.md — entry under ## Next
• examples/customize/build_graph/components/loaders/liteparse_loader.py — usage example
• tests/unit/experimental/components/test_liteparse_loader.py — 9 unit tests (fully mocked)
• tests/unit/experimental/components/test_liteparse_loader_integration.py — 5 integration tests (real liteparse; auto-skipped when absent)

Usage

from neo4j_graphrag.experimental.components.liteparse_loader import LiteParseLoader
from neo4j_graphrag.experimental.pipeline.kg_builder import SimpleKGPipeline

pipeline = SimpleKGPipeline(
    llm=...,
    driver=...,
    embedder=...,
    file_loader=LiteParseLoader(ocr_enabled=True),  # or LiteParseLoader() for text PDFs
    from_file=True,
)
await pipeline.run_async(file_path="document.pdf")

Test plan

• uv run pytest tests/unit/experimental/components/test_liteparse_loader.py — 9 unit tests pass without liteparse installed
• pip install "neo4j-graphrag[liteparse]" && uv run pytest tests/unit/experimental/components/test_liteparse_loader_integration.py — 5 integration tests pass with liteparse installed
• Existing test_data_loader.py tests unaffected