Modernize build system: Rust stable + Python 3.8+ + maturin + uv

[athoune]

Summary

This project has been abandoned for several years and requires Rust nightly and Python 2.7 support. I've done a complete modernization of the build system and I'm proposing a PR for your review.

Changes Made

1. Migrate from Rust nightly to stable ()

• Removed #![feature(core_intrinsics)] and #![crate_type = "dylib"]
• Replaced std::intrinsics::type_name with std::any::type_name (stable since 1.38)
• Replaced deprecated err.description() with format!("{}", err)
• Added explicit "C" ABI to extern fn declarations in macros
• Fixed unused_must_use warnings with drop() in free functions
• Removed unused std::error::Error imports

2. Drop Python 2.7 support (fd97538)

• Removed py27 from tox.ini envlist
• Updated appveyor.yml: Python 2.7 → 3.9, Rust nightly → stable
• Removed from __future__ import print_function from rust_setuptools.py
• Updated docs and README to require Python >= 3.8

3. Migrate build system to maturin + uv (145932e)

• Replaced legacy setup.py/milksnake with modern maturin CFFI backend
• Added pyproject.toml with proper metadata and dependencies
• Renamed Rust crate to _rust_fst to avoid Python package name collision
• Updated rust_fst/lib.py import: from ._native → from ._cffi
• Removed setup.py, rust_setuptools.py, test-requirements.txt, tox.ini
• Rewrote build-wheels.sh to use maturin + uv

4. Code quality fixes (4a9d89d, 9738fa3)

• Added rust_fst/_cffi.py wrapper to isolate CFFI imports
• Added C99 typedefs to rust_fst.h for valid ISO C
• Documented build.rs fragility (cbindgen can't handle generic types)
• Updated README.md, docs/index.rst, and appveyor.yml

Test Results

All 38 tests pass:

uv run pytest tests/ -v
============================== 38 passed in 0.44s ==============================

Build Verification

maturin build --release -o /tmp/wheelhouse
# Produces: rust_fst-0.3.0-py3-none-macosx_11_0_arm64.whl

Current Status

The work is on a branch in my fork: modernize-build-system

I'm not creating the PR yet — I'd like your feedback first. If you're interested, I can open the PR for review.

Known Limitations

• The C header (rust_fst.h) is hand-written because cbindgen cannot handle generic Rust types (`SetBuilder<BufWriter*>). It must be kept in sync manually.
• The Rust crate is named _rust_fst (not rust_fst) to avoid collision with the Python package when maturin generates CFFI bindings.
• CI files (.travis.yml, appveyor.yml) are updated but not fully tested with the new build system.