fix: Add support for multibyte strings

[neznaika0]

Description

• Unicode namespases App\Контроллеры\Админ allowed in Namespaces::truncate()
• Now $view->excerpt('<unicode string>') and excerpt('<unicode string>') works correctly with characters, not bytes.

Can someone clarify why excerpt() adds an extra space and removes a character from the string? See tests - It sad So some nice, Это печ льно. И вот несколько. Missing dot and "a".

CodeIgniter4/tests/system/Helpers/TextHelperTest.php

Line 395 in 6ee2083

$result = ' Once upon a time, a framework had no tests. It sad So some nice people began to write tests. The more time that went on, the happier it became. ...';

CodeIgniter4/tests/system/Helpers/TextHelperTest.php

Line 399 in 6ee2083

$multibyteResult = ' Давным-давно во фреймворке не было тестов. Это печ льно. И вот несколько хороших людей начали писать тесты. Чем больше времени проходило, тем ...';

Checklist:

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

[paulbalandan]

Thank you, @neznaika0