Update for_helpers.py

Author: BobTheBuidler

mypyc/irbuild/for_helpers.py

@@ -1211,7 +1211,10 @@ def get_expr_length(expr: Expression) -> int | None:
         and expr.node.has_explicit_value
     ):
         return len(expr.node.final_value)
-    # TODO: extend this, passing length of listcomp and genexp should have worthwhile performance boost
+    # TODO: extend this, passing length of listcomp and genexp should have worthwhile
+    # performance boost and can be (sometimes) figured out pretty easily. set and dict
+    # comps *can* be done as well but will need special logic to consider the possibility
+    # of key conflicts
     return None