add flake8 and improve nvim-tree

modules/programming/python.nix

@@ -6,6 +6,7 @@
       # python310 # Standard Python interpreter
       nodePackages.pyright # Python language server
       black # Python formatter
+      python310Packages.flake8 # Python linter
     ];
 
     programs.fish.shellAbbrs = { py = "python3"; };