groupthm: speedup caching

replacing # in cached expressions only
    when necessary speeds up usage

src/environments/groupthm/groupthm.dtx

@@ -2616,7 +2616,7 @@
 %    Cache this definition for re-runs of \LaTeX.
 % 
 %    \begin{macrocode}
-    \@@_cache:n
+    \@@_cache_slow:n
       {
         \csname @@_define_family_options:nnnn \endcsname { #1 } { #2 } { #3 } { #4 }
       }
@@ -2864,7 +2864,18 @@
 %       for details.
 %
 %    \begin{macrocode}
-    \cs_new:Npn \@@_cache:n #1
+    \cs_set_eq:NN \@@_cache:n \@@_cache_auxfile:n
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+%
+% \begin{macro}{\@@_cache_slow:n}
+%		 
+%     
+%
+%    \begin{macrocode}
+  \cs_new:Npn \@@_cache_slow:n #1
     {
       \tl_set:Nn \l_tmpa_tl
         {
@@ -2889,7 +2900,7 @@
             \tl_use:N \g_@@_lazy_document_tl
           }
           {
-              \cs_show:N \g_@@_lazy_auxfile_tl
+            \exp_args:NNV \iow_now:Nn \l_my_iow \g_@@_lazy_auxfile_tl
               \benchmark_once:n
                 {
                   \tl_use:N \g_@@_lazy_auxfile_tl