chore(release): v1.4.0 (#97)

Minor bump for the common-library refactor (#94) and the optional
TBB parallelisation of classic Patchwork (#95). pypatchworkpp.patchwork
gains 1.73x (120 -> 208 Hz on KITTI seq 00, i7-12700). pypatchworkpp.patchworkpp
stays sequential after measurement — see #96 for the why.

TBB is an optional build dependency: missing TBB falls back to a
sequential loop with a CMake STATUS message; CI/wheel builds keep
working without libtbb-dev installed.

Bumps:
- python/pyproject.toml  1.3.1 -> 1.4.0
- cpp/CMakeLists.txt     1.3.1 -> 1.4.0

CHANGELOG.md updated with the full v1.4.0 entry.

See #94, #95, #96.

Author: LimHyungTae

CHANGELOG.md

@@ -1,5 +1,81 @@
 # Changelog
 
+## v1.4.0
+
+### Refactor — shared `common` library + optional TBB parallelisation
+
+`cpp/common/` is a new tiny static library holding the parts of the
+codebase that are independent of the Patchwork / Patchwork++
+pipelines:
+
+- `cpp/common/include/patchwork/types.h` — `PointXYZ`, `PCAFeature`
+  (now carries the `principal_` field for parity with the original
+  Patchwork repo), `PatchStatus`.
+- `cpp/common/include/patchwork/plane_fit.h` +
+  `cpp/common/src/plane_fit.cpp` — the SVD-based `estimate_plane`,
+  plus `xy2theta`, `xy2radius`, `point_z_cmp`.
+
+Both `cpp/patchwork/` and `cpp/patchworkpp/` now link this library
+and the three drifted copies of the plane-fit math are collapsed to
+one canonical implementation. Fix 2 in #90 was a concrete example of
+that drift causing a real bug.
+
+### Perf — `pypatchworkpp.patchwork` is now multi-threaded
+
+Classic Patchwork's main loop uses `tbb::parallel_for` over all
+`(zone, ring, sector)` patches when TBB is available, with a serial
+reduction afterwards that walks the outcome buffer in deterministic
+order so numerical results are byte-identical to the sequential path.
+
+Measured on KITTI seq 00 (i7-12700, 24 logical cores):
+
+| Configuration | Median ms/frame | Median Hz |
+| -- | --: | --: |
+| `--method patchwork` single-thread (taskset -c 0) | 8.31 | 120.4 |
+| `--method patchwork` parallel (TBB default scheduler) | **4.81** | **207.8** |
+
+**1.73× speedup**. TBB is an **optional** build dependency: missing
+TBB causes a CMake STATUS message and falls back to a sequential
+loop (no FATAL_ERROR), so existing CI / wheel builds continue to
+work even when `libtbb-dev` is not installed.
+
+### Perf — `pypatchworkpp.patchworkpp` stays sequential (intentional)
+
+The same TBB pattern was applied to Patchwork++'s main loop and
+benchmarked at 1 / 2 / 4 / 8 / 16 / 24 threads. **Every multi-thread
+configuration was slower** than single-thread (111 Hz → 93 Hz at 2
+threads, → 69 Hz at 24 threads). Root cause: per-patch work is small
+(~14 µs avg) and dominated by short-lived `std::vector` / `Eigen`
+allocations inside R-VPF + R-GPF, so concurrent malloc serialises on
+the heap allocator. Patchwork++ remains sequential. Issue #96
+documents the measurement and the conditions under which we'd
+revisit (thread-aware allocator, slab-allocated per-worker scratch,
+or a real user CPU complaint).
+
+### Adds
+
+- `python/examples/bench_hz.py` — per-frame timing harness reporting
+  median / mean / p95 / p99 ms and Hz from `getTimeTaken()`. Useful
+  for future perf work.
+
+### Numerical equivalence
+
+KITTI 00-10 full sweep (23,201 frames), Patchwork++ paper protocol,
+v1.3.1 → v1.4.0:
+
+| Method | F1 v1.3.1 | F1 v1.4.0 | Δ |
+| --- | --- | --- | --- |
+| `--method patchwork` | 96.0172 | 96.0172 | 0 (byte-identical) |
+| `--method patchworkpp` | 96.2918 | 96.2919 | +0.0001 (float noise) |
+
+Both well within the ±0.05 budget set in the refactor plan.
+
+### References
+
+- #94 — PR (refactor: extract common library)
+- #95 — PR (perf: TBB on classic Patchwork)
+- #96 — Issue (why Patchwork++ has no TBB)
+
 ## v1.3.1
 
 ### Bug fix — `pypatchworkpp.patchworkpp` (Patchwork++)

cpp/CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.11)
-project(patchworkpp VERSION 1.3.1)
+project(patchworkpp VERSION 1.4.0)
 
 option(USE_SYSTEM_EIGEN3 "Use system pre-installed Eigen" OFF)
 option(INCLUDE_CPP_EXAMPLES "Include C++ example codes, which require Open3D for visualization" OFF)

python/pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "pypatchworkpp"
-version = "1.3.1"
+version = "1.4.0"
 requires-python = ">=3.8"
 description = "ground segmentation"
 dependencies = [