update changelog

Author: Adria Labay

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Change the structure of block diagonalization functions, using `BlockDiagonalForm` struct and changing the function name from `bdf` to `block_diagonal_form`. ([#349])
 - Add **GPUArrays** compatibility for `ptrace` function, by using **KernelAbstractions.jl**. ([#350])
+- Implement `mean_occupation`, `remove_coherence` and extend `get_coherence` to support composite states.
 
 ## [v0.24.0]
 Release date: 2024-12-13