rand_xoshiro: Update changelog

Author: vks

rand_xoshiro/CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+### Changed
+- Shrink the code size of the all-zero-seed fallback by replacing the per-RNG
+  `SplitMix64::seed_from_u64(0)` call with a single shared constant.
+
 ## [0.8.0] - 2026-02-01
 ### Changes
 - Use Edition 2024 and MSRV 1.85 ([#73])