Incorrect type on Source->timestamp

The PHPDoc type for the field $timestamp is set as int in Smarty\Template\Source, however there are many examples that exist which set the timestamp to false in the event that there is no source file found.

Here are some notable examples:

src/Resource/StringEval

public function populate(\Smarty\Template\Source $source, \Smarty\Template $_template = null)
 {
    $source->uid = sha1($source->name);
    $source->timestamp = $source->exists = true;
 }

src/Resource/StreamPlugin

public function populate(Source $source, ?Template $_template = null) {
    $source->uid = false;
    $source->content = $this->getContent($source);
    $source->timestamp = $source->exists = !!$source->content;
}

src/Resource/FilePlugin

public function populate(Source $source, ?Template $_template = null) {
    $source->uid = sha1(
        $source->name . ($source->isConfig ? $source->getSmarty()->_joined_config_dir :
        $source->getSmarty()->_joined_template_dir)
     );

    if ($path = $this->getFilePath($source->name, $source->getSmarty(), $source->isConfig)) {
         if (isset($source->getSmarty()->security_policy) && is_object($source->getSmarty()->security_policy)) {
            $source->getSmarty()->security_policy->isTrustedResourceDir($path, $source->isConfig);
        }
        $source->exists = true;
        $source->timestamp = filemtime($path);
    } else {
        $source->timestamp = $source->exists = false;
    }
}

If this is intended, the type should likely be changed to int|false.

Inspect the PHPDoc for $timestamp in Smarty\Template\Source and compare it with the populate methods in src/Resource/StringEval, src/Resource/StreamPlugin, and src/Resource/FilePlugin. Update the documented type if the false value is intended, then run the relevant existing test suite to verify the change.