Add dfft experimental BFFT workspace: native library, Python bindings, kernels, docs, CI, and tests

[falseywinchnet]

Motivation

• Introduce a self-contained experimental DFFT (dragon BFFT) workspace to prototype explicit boundary ownership, scheduling and arena experiments without altering the repository root.
• Provide a complete build/test/documentation surface for the experimental tree so native kernels, Python bindings, and benchmarking tooling can be exercised reproducibly.

Description

• Add a full dfft/ subtree with the BFFT C API and C++ wrappers (include/bfft/*.h/.hpp), native implementations (src/*.cpp, including bruun_kernel.hpp, bodft_kernel.hpp and supporting generated tables), and the new BODFT kernel implementation.
• Provide Python bindings and tooling: a ctypes/ctypes+numba loader (bfft/_core.py, bfft/numba_support.py), a packaging build hook (setup.py / pyproject.toml), and a high-level bfft package shim (bfft/__init__.py, _core.py) plus an STFT convenience implementation (stft.py) and validation/benchmark scripts (benchmarks/*, scripts/*).
• Add extensive examples, benchmarks and probes (many examples/ and tests/ programs) including correctness tests, SFDR/support probes, and audio mag/phase benchmarks, plus documentation under documentation/ and DRAGON_BOUNDARIES.md describing the experimental design intentions.
• Add build infrastructure: Makefile, CMakeLists.txt, pkgconfig/bfft.pc.in, MANIFEST.in, FUNDING.yml, .readthedocs.yaml, and GitHub Actions CI (.github/workflows/ci.yml) that runs both the Makefile and CMake builds across platforms and runs tests; include a .gitignore and LICENSE (MIT).
• Add developer tooling and generated resources: generator script for phase/sincos tables (tools/gen_phase_slope_tables.py), pre-generated lookup headers, an interactive agent loop helper (scripts/agent-loop.sh), and many performance-oriented sources (AVX2/FMA-enabled paths guarded by backend detection macros).

Testing

• Continuous integration: added GitHub Actions workflow dfft/.github/workflows/ci.yml that runs make and make test on ubuntu-latest and performs multi-platform CMake configure / build / ctest on Linux/macOS/Windows; the workflow is configured to stage and verify the Makefile and CMake install targets.
• Local/automated checks exercised during development: ran make and make test (Makefile path) and CMake cmake --build + ctest for the CMake build; the tests included tests/correctness, tests/api_c, and the various probe/benchmark binaries; these automated builds and tests completed successfully.
• Python checks: benchmarks/stft_validation.py and the ctypes/numba binding smoke paths are included and used for validation; package build via pip install . compiles the native shared library through the provided setup.py build hook (used in CI as part of the make/CMake stages).

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Codex Task