Update CHANGELOG.md

Author: agriyakhetarpal

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ## Optimizations
 
+- Implemented memoization via `cache` and `cached_property` from functools ([#2465](https://github.com/pybamm-team/PyBaMM/pull/2465))
 - `ParameterValues` now avoids trying to process children if a function parameter is an object that doesn't depend on its children ([#2477](https://github.com/pybamm-team/PyBaMM/pull/2477))
 - Added more rules for simplifying expressions, especially around Concatenations. Also, meshes constructed from multiple domains are now cached ([#2443](https://github.com/pybamm-team/PyBaMM/pull/2443))
 - Added more rules for simplifying expressions. Constants in binary operators are now moved to the left by default (e.g. `x*2` returns `2*x`) ([#2424](https://github.com/pybamm-team/PyBaMM/pull/2424))