Update dependency from marathon to marathon-train

Replaced 'marathon[grain]' dependency with 'marathon-train[grain]' in pyproject.toml.

Othwerwise the dependency resolver will compare to the marathon package on pypi...

Author: PicoCentauri

pyproject.toml

@@ -11,7 +11,7 @@ dependencies = [
     "jax",
     "jax-pme @ git+https://github.com/lab-cosmo/jax-pme.git",
     "jaxtyping",
-    "marathon[grain] @ git+https://github.com/sirmarcel/marathon.git@release/v0.2.0",
+    "marathon-train[grain] @ git+https://github.com/sirmarcel/marathon.git@release/v0.2.0",
     "optax",
 ]
 dynamic = ["version"]