fixes #24666; Compliation error when formatting a complex number

Author: ringabout

lib/pure/complex.nim

@@ -33,7 +33,7 @@ runnableExamples:
 {.push checks: off, line_dir: off, stack_trace: off, debugger: off.}
 # the user does not want to trace a part of the standard library!
 
-import std/[math, strformat]
+import std/[math, strformat, strutils]
 
 type
   Complex*[T: SomeFloat] = object