Python-specific QoL improvements

[b-rodrigues]

If using uv to manage package, automatically add:

shellHook = ''
   # Export LD_LIBRARY is required for python packages that dynamically load libraries, such as numpy 
   export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath (with pkgs; [ zlib gcc.cc glibc stdenv.cc.cc ])}":LD_LIBRARY_PATH;
   ...
   '';

add some way to easily add the following shellHook when developing packages:

shellHook = ''
  export PYTHONPATH=$PWD/pyclean/src:$PYTHONPATH
'';