fix(str): correct loop variable checks and use mb_strlen in after_last

Author: xHeaven

packages/support/src/Str/functions.php

@@ -257,7 +257,7 @@ function after_last(Stringable|string $string, Stringable|string|array $search):
             return $string;
         }
 
-        return mb_substr($string, $farthestPosition + strlen($foundSearch));
+        return mb_substr($string, $farthestPosition + mb_strlen($foundSearch));
     }
 
     /**
@@ -371,7 +371,7 @@ function replace_first(Stringable|string $string, array|Stringable|string $searc
         $search = normalize_string($search);
 
         foreach (Arr\wrap($search) as $item) {
-            if ($search === '') {
+            if ($item === '') {
                 continue;
             }
 
@@ -421,7 +421,7 @@ function replace_end(Stringable|string $string, array|Stringable|string $search,
         $search = normalize_string($search);
 
         foreach (Arr\wrap($search) as $item) {
-            if ($search === '') {
+            if ($item === '') {
                 continue;
             }
 
@@ -443,7 +443,7 @@ function replace_start(Stringable|string $string, array|Stringable|string $searc
         $string = (string) $string;
 
         foreach (Arr\wrap($search) as $item) {
-            if ($search === '') {
+            if ($item === '') {
                 continue;
             }