experiment: shellfilter flush of stdout

src/modules/shellfilter-999999.0a1.0.tm

@@ -3185,6 +3185,8 @@ namespace eval shellfilter {
                     #set newbytes [encoding convertto utf-16 $stringrep]
                     #puts -nonewline $outchan $newbytes
                     puts -nonewline $outchan $outchunk
+                    #jmn test 2025
+                    flush $outchan
                 }
             }