fix: toRawArray() should convert DateTime objects to strings

Fixes #8302

When a date field listed in $dates is set on an Entity, __set()
converts it to a Time object via mutateDate(). However, toRawArray()
returned $this->attributes directly without converting Time/DateTime
objects back to strings.

This caused toRawArray() to return Time objects for date fields
that were manually set, e.g.:
  $user->updated_at = '2023-12-12 12:12:12';
  $user->toRawArray(); // 'updated_at' => Time object (bug)

Solution:
- Add DateTimeInterface check at the top of the convert closure in
  toRawArray(), converting DateTime objects to strings via __toString()
- Always run attributes through convert closure in the !onlyChanged
  path instead of returning $this->attributes directly
- Apply convert closure to non-recursive changed values too

Ref: #8302

Author: jalexiscv

system/Entity/Entity.php

@@ -233,6 +233,11 @@ public function toArray(bool $onlyChanged = false, bool $cast = true, bool $recu
     public function toRawArray(bool $onlyChanged = false, bool $recursive = false): array
     {
         $convert = static function ($value) use (&$convert, $recursive) {
+            // Always convert DateTime objects to string for raw output
+            if ($value instanceof DateTimeInterface) {
+                return (string) $value;
+            }
+
             if (! $recursive) {
                 return $value;
             }
@@ -261,9 +266,7 @@ public function toRawArray(bool $onlyChanged = false, bool $recursive = false):
 
         // When returning everything
         if (! $onlyChanged) {
-            return $recursive
-                ? array_map($convert, $this->attributes)
-                : $this->attributes;
+            return array_map($convert, $this->attributes);
         }
 
         // When filtering by changed values only
@@ -335,7 +338,7 @@ public function toRawArray(bool $onlyChanged = false, bool $recursive = false):
             }
 
             // non-recursive changed value
-            $return[$key] = $value;
+            $return[$key] = $convert($value);
         }
 
         return $return;