Make changelog

Author: albertomercurio

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)
 
+- Add `spre` and `spost` methods for `ComposedOperator` and cache propagator in every time evolution solver. ([#596])
+
 ## [v0.39.0]
 Release date: 2025-11-17
 
@@ -374,3 +376,4 @@ Release date: 2024-11-13
 [#588]: https://github.com/qutip/QuantumToolbox.jl/issues/588
 [#589]: https://github.com/qutip/QuantumToolbox.jl/issues/589
 [#591]: https://github.com/qutip/QuantumToolbox.jl/issues/591
+[#596]: https://github.com/qutip/QuantumToolbox.jl/issues/596