[v2.0] Phase 1: Project setup & build infrastructure

[fsecada01]

Set up the Maturin build system and Rust project structure alongside the existing Python layout.

Wiki: Phase 1 detail
Branch: feature/rust-backend

Tasks

• 1.1 Update pyproject.toml — swap build backend to maturin>=1.4,<2.0; add [tool.maturin] config
• 1.2 Create Cargo.toml — text_spitter_rust crate, PyO3 + Rayon deps, release profile
• 1.3 Create TextSpitter/splitters.py — empty module skeleton (implementation in Phase 3)
• 1.4 Add maturin to dev dependencies: uv add --dev maturin
• 1.5 Verify maturin develop builds without error; existing uv run pytest tests/ still green

Notes

• Do not rename or move existing TextSpitter/ modules
• The Rust extension is named text_spitter_rust to avoid import collision with the TextSpitter package