RATE Function Permits Floating Point NPER

Suggested by PR PHPOffice#848 from @markkimsal. The RATE calculation had already been corrected, so that part of the PR was unnecessary, however one of the tests included a floating point value for Number of Periods, which Excel permits. PhpSpreadsheet till now expected that parameter to be an integer. This is trivially changed with some tests added.

src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Interest.php

@@ -165,7 +165,7 @@ public static function rate(
         $guess = ($guess === null) ? 0.1 : Functions::flattenSingleValue($guess);
 
         try {
-            $numberOfPeriods = CashFlowValidations::validateInt($numberOfPeriods);
+            $numberOfPeriods = CashFlowValidations::validateFloat($numberOfPeriods);
             $payment = CashFlowValidations::validateFloat($payment);
             $presentValue = CashFlowValidations::validatePresentValue($presentValue);
             $futureValue = CashFlowValidations::validateFutureValue($futureValue);
@@ -193,7 +193,7 @@ public static function rate(
         return $close ? $rate : ExcelError::NAN();
     }
 
-    private static function rateNextGuess(float $rate, int $numberOfPeriods, float $payment, float $presentValue, float $futureValue, int $type): string|float
+    private static function rateNextGuess(float $rate, float $numberOfPeriods, float $payment, float $presentValue, float $futureValue, int $type): string|float
     {
         if ($rate == 0.0) {
             return ExcelError::NAN();

tests/data/Calculation/Financial/RATE.php

@@ -29,6 +29,18 @@
         -250,
         5000,
     ],
+    [
+        0.017929869399484,
+        24.99,
+        -250,
+        5000,
+    ],
+    [
+        0.016581855,
+        24.5,
+        -250,
+        5000,
+    ],
     [
         0.016550119066711999,
         24,