docs: cut CHANGELOG 0.3.3

Stamp the median-consensus merge and arc-length start-rotation work as
0.3.3 and open a fresh Unreleased section.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: wrignj08

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+## [0.3.3] - 2026-07-02
+
 ### Changed
 - Start-point variants are now merged by a per-point median consensus instead of a geometric union. Douglas-Peucker is start-vertex dependent, so the four rotated variants disagree slightly about where a feature's vertices land; the union superimposed those disagreements, whereas the median resamples the variants to a common point count, brings them into phase via an FFT cross-correlation, and takes the coordinate-wise median — a start-invariant consensus that outvotes a single bad variant instead of averaging toward it. This is also faster than the union it replaces (~1.3x end-to-end at the default 3 iterations, ~1.4x at 5, on `examples/Water.gpkg`). The median sits at the consensus interior rather than the outer envelope, so the merged ring is marginally smaller before area preservation restores it (with `preserve_area=True`); with `preserve_area=False` the small reduction is left as-is.
 - Faster smoothing with no meaningful change to output. Start-point variants now begin at evenly spaced arc-length positions, computed by interpolating a single new start vertex, rather than rotating to a vertex index on a fully densified ring. The old path segmentized the whole ring only so that index-based rotation would land on evenly spaced points — but every vertex it added was collinear and immediately stripped by the following Douglas-Peucker. Feeding DP just the original vertices plus one cuts its input roughly 3.4x and the simplify step ~3.5x on `examples/Water.gpkg` (total single-core CPU work ~4.4s → ~2.7s, about 1.25x faster end-to-end at the default 3 iterations). The per-point median phase-alignment and Chaikin corner cutting also replace `numpy.roll` with a slice-based cyclic shift (bit-identical, fewer allocations). Output is unchanged within tolerance (per-polygon area drift ≤ 0.01%, worst concave turn unchanged).