fix: Time::createFromTimestamp() returns Time with UTC

[kenjis]

Description From https://github.com/codeigniter4/shield/pull/1027/files#r1488969384

Time::createFromTimestamp() returns Time with the timezone UTC. This behavior is misleading.

--- a/app/Config/App.php
+++ b/app/Config/App.php
@@ -109,7 +109,7 @@ class App extends BaseConfig
      * @see https://www.php.net/manual/en/timezones.php for list of timezones
      *      supported by PHP.
      */
-    public string $appTimezone = 'UTC';
+    public string $appTimezone = 'Asia/Tokyo';
 
     /**
      * --------------------------------------------------------------------------

        //        UTC 1999-12-31 15:00:00
        // Asia/Tokyo 2000-01-01 00:00:00
        $timestamp = 946652400;

        $time = DatetimeCast::get($timestamp);

        return $time->format('Y-m-d H:i:s'); // 1999-12-31 15:00:00

Carbon sets the current timezone.

You can create instances from unix timestamps. createFromTimestamp() create a Carbon instance equal to the given timestamp and will set the timezone as well or default it to the current timezone. https://carbon.nesbot.com/docs/#api-instantiation

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [x] User guide updated
• [x] Conforms to style guide

[kenjis]

Added docs.