This PR adds complete support for Python 3.14 free-threaded builds (python3.14t) to fix installation and build issues where the package would fail to build wheels or generate config files for free-threaded Python interpreters.

Changes Made

Core Implementation

• Free-threaded Detection: Added is_free_threaded_python() function that correctly identifies free-threaded Python by checking if the executable name ends with 't' or 't.exe'
• Dynamic Config File Naming: Enhanced the build system to generate config-3t.py for free-threaded builds versus config-3.py for standard builds, with fallback logic for compatibility
• Build System Integration: CMake arguments now properly handle free-threaded executables through -DPYTHON3_EXECUTABLE and -DPYTHON_DEFAULT_EXECUTABLE parameters

Bug Fixes

• Fixed scripts/init.py: Added missing imports (import os, import sys) and properly defined LOADER_DIR variable that was causing import errors
• Updated Documentation: Added Python 3.14 to the supported versions list in README.md

Metadata Updates

• Setup.py Classifiers: Added "Programming Language :: Python :: 3.14" classifier for proper PyPI metadata

Example Usage

The implementation automatically detects free-threaded Python builds:

# Standard Python 3.14
$ python3.14 setup.py bdist_wheel
# → Uses config-3.py

# Free-threaded Python 3.14
$ python3.14t setup.py bdist_wheel  
# → Uses config-3t.py, detects free-threaded mode

Testing

All functionality has been validated to ensure:

• ✅ Free-threaded detection works for various executable patterns (python3.14t, python3.14t.exe)
• ✅ Config file naming generates correct filenames based on Python type
• ✅ CMake arguments properly pass free-threaded executable paths
• ✅ Build system works for both standard and free-threaded Python 3.14
• ✅ No regression in existing functionality

This resolves build failures when attempting to create wheels with free-threaded Python 3.14 interpreters and ensures the package works correctly with Python's new free-threading feature.

This pull request was created as a result of the following prompt from Copilot chat.

Adds support for Python 3.14 free-threaded builds (python3.14t) in setup.py. This fixes an installation/build issue where the package would fail to build wheels or generate config files for free-threaded Python 3.14. Key changes: setup.py now detects the free-threaded executable, handles config file naming, and ensures build scripts and config files work for both standard and free-threaded Python 3.14.

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