docs: Replace type mixed in system.

Author: ping-yee

system/BaseModel.php

@@ -1711,7 +1711,7 @@ protected function transformDataToArray($data, string $type): array
      *
      * @param string $name Name
      *
-     * @return mixed
+     * @return array|bool|int|object|string|null
      */
     public function __get(string $name)
     {

system/CodeIgniter.php

@@ -732,7 +732,7 @@ public static function cache(int $time)
      * Caches the full response from the current request. Used for
      * full-page caching for very high performance.
      *
-     * @return mixed
+     * @return bool
      */
     public function cachePage(Cache $config)
     {

system/Common.php

@@ -65,8 +65,8 @@ function app_timezone(): string
      *    cache()->save('foo', 'bar');
      *    $foo = cache('bar');
      *
-     * @return CacheInterface|mixed
-     * @phpstan-return ($key is null ? CacheInterface : mixed)
+     * @return array|bool|CacheInterface|float|int|object|string|null
+     * @phpstan-return ($key is null ? CacheInterface : array|bool|float|int|object|string|null)
      */
     function cache(?string $key = null)
     {
@@ -1003,7 +1003,7 @@ function session(?string $val = null)
      *  - $timer = service('timer')
      *  - $timer = \CodeIgniter\Config\Services::timer();
      *
-     * @param mixed ...$params
+     * @param array|bool|float|int|object|string|null ...$params
      *
      * @return object
      */
@@ -1017,7 +1017,7 @@ function service(string $name, ...$params)
     /**
      * Always returns a new instance of the class.
      *
-     * @param mixed ...$params
+     * @param array|bool|float|int|object|string|null ...$params
      *
      * @return object|null
      */

system/Model.php

@@ -792,7 +792,7 @@ protected function objectToRawArray($data, bool $onlyChanged = true, bool $recur
      *
      * @param string $name Name
      *
-     * @return mixed
+     * @return array|BaseBuilder|bool|int|object|string|null
      */
     public function __get(string $name)
     {
@@ -821,7 +821,7 @@ public function __isset(string $name): bool
      * Provides direct access to method in the builder (if available)
      * and the database connection.
      *
-     * @return mixed
+     * @return array|BaseBuilder|bool|float|int|object|string|null
      */
     public function __call(string $name, array $params)
     {