docs: fix @return types

Author: kenjis

system/Common.php

@@ -63,6 +63,7 @@ function app_timezone(): string
      *    $foo = cache('bar');
      *
      * @return CacheInterface|mixed
+     * @phpstan-return ($key is null ? CacheInterface : mixed)
      */
     function cache(?string $key = null)
     {
@@ -196,7 +197,7 @@ function command(string $command)
     /**
      * More simple way of getting config instances from Factories
      *
-     * @return mixed
+     * @return object|null
      */
     function config(string $name, bool $getShared = true)
     {
@@ -376,7 +377,7 @@ function dd(...$vars)
      *
      * @param string|null $default
      *
-     * @return mixed
+     * @return bool|string|null
      */
     function env(string $key, $default = null)
     {
@@ -952,7 +953,7 @@ function session(?string $val = null)
      *
      * @param mixed ...$params
      *
-     * @return mixed
+     * @return object
      */
     function service(string $name, ...$params)
     {
@@ -966,7 +967,7 @@ function service(string $name, ...$params)
      *
      * @param mixed ...$params
      *
-     * @return mixed
+     * @return object|null
      */
     function single_service(string $name, ...$params)
     {
@@ -1076,7 +1077,7 @@ function stringify_attributes($attributes, bool $js = false): string
      * If no parameter is passed, it will return the timer instance,
      * otherwise will start or stop the timer intelligently.
      *
-     * @return mixed|Timer
+     * @return Timer
      */
     function timer(?string $name = null)
     {

system/Database/Database.php

@@ -35,7 +35,7 @@ class Database
      * Parses the connection binds and returns an instance of the driver
      * ready to go.
      *
-     * @return mixed
+     * @return BaseConnection
      *
      * @throws InvalidArgumentException
      */