reproductibility: pin specific NUR-kapack commit in nix file

default.nix

-{ 
-  kapack ? import ( fetchTarball "https://github.com/oar-team/nur-kapack/archive/master.tar.gz") {}
-}: 
+# Reproductibility: pin a specific commit of nur-kapack repository
+# This one contains Batsim v4.10 and Simgrid v3.31
+{ kapack ? import (fetchTarball {
+    url = "https://github.com/oar-team/nur-kapack/archive/b3611a0e7aadd69ca961d14639e8470df19f8564.tar.gz";
+    sha256 = "sha256:0rjwq0csb1z79jakicl638xa8r1wwyf8vd8ymrpfa1waiw7vfpc5";
+  }) {}
+}:
 
 with kapack.pkgs;
 
@@ -12,20 +16,16 @@ let self = rec {
       url = "https://gitlab.irit.fr/sepia-pub/mael/batmen.git";
       rev = version;
       sha256 = "0b8rycph0s2ir176582llyqyszqznlrsrc10q2hzjq9wmggzkv3g";
-
     };
   });
 
   exp_env = mkShell rec {
     name = "exp_env";
     buildInputs = [
-      # simulator
-      kapack.batsim
-      # scheduler implementations
-      batmen
-      # misc. tools to execute instances
-      kapack.batexpe
-      kapack.evalys
+      kapack.batsim-410   # data center simulator
+      batmen              # scheduler + user simulator
+      kapack.batexpe      # tool to execute batsim instances
+      kapack.evalys       # for data visualization
       (python3.withPackages 
         (ps: with ps; with python3Packages; [jupyter ipython pandas numpy matplotlib
           plotly pip tabulate pytz isodate ordered-set yattag])