Final part of breaking down the Engineering class for Excel Engineering functions into smaller individual/group classes (#1940)

* Final breaking down the Engineering class for Excel Engineering functions into smaller individual/group classes
* Additional unhappy path tests for Complex Number functions
* Fix return docblocks for floats to allow for error strings

tests/data/Calculation/Engineering/IMLOG10.php

@@ -1,10 +1,16 @@
 <?php
 
+use PhpOffice\PhpSpreadsheet\Calculation\Functions;
+
 return [
     [
         '1.13290930735019+0.187055234944717j',
         '12.34+5.67j',
     ],
+    [
+        Functions::NAN(),
+        'Invalid Complex Number',
+    ],
     [
         '9.83122969386706+0.682188176920927i',
         '-12.34E-5+6.78E9i',
@@ -58,7 +64,7 @@ return [
         'i',
     ],
     [
-        '#NUM!',
+        Functions::NAN(),
         '0',
     ],
     [