include transverse permittivity matrix in layer solve result

Author: mfschubert

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 - Restructure codebase to integrate code originally in the `_orig` submodule within the main `src/fmmax` modules, separating the code available under the two licenses to the top (AGPL) and bottom (MIT) of each file.
+- Include `transverse_permittivity_matrix` in the `LayerSolveResult`.
 
 ## 1.4.2 (July 10, 2025)
 - Avoid use of `jax.pure_callback` in the eigendecomposition. This requires jax newer than 0.4.36.