Update encode method to use type hinting for string|Response object

[joanhey]

Available from PHP 8.0.

EDIT: string|Response|ServerSentEvents string|Stringable
With only type hint string, any class that implements stringable can be passed, so we are not limiting the classes. And we can simplify the send() code as always is string. But for now it's OK.

PD: later we need to check the TcpConnection::send() why the $sendBuffer receive null. This variable now is mixed need to be limited to string|Stringable.
For now use a fast fix $sendBuffer ??= '';

[joanhey]

Interesting journey with this code.

Testing string|Stringable type hint.

With only string we can pass strings or any class that implements Stringable without any problem.

class str implements stringable {
    function __tostring(){
        return 'Hola';
    }
}

$b = new str();

function test(string $input = '') {
    if (is_string($input)) echo "String";
    if (is_a($input, 'Stringable')) echo "Object";
    var_dump($input);
}

test($b);

// Return:
Stringstring(4) "Hola"

With string|Stringable the same, but change:

class str implements stringable {
    function __tostring(){
        return 'Hola';
    }
}

$b = new str();

function test(string|Stringable $input = '') {
    if (is_string($input)) echo "String";
    if (is_a($input, 'Stringable')) echo "Object";  // or is_a($input, 'str')
    var_dump($input);
    echo $input;
}

test($b);

// Return:
Objectobject(str)#1 (0) {
}
Hola

Here only change to string when echo or (string).

And seems that phpstan fail with this code.

[joanhey]

In my humble opinion, we can refactor the Http::encode()

Checking the code:

• https://github.com/walkor/workerman/pull/1150/changes#diff-f1e0bc96c431d22de194587082a047639ab3d2b4a26b62a8dee62ff7f86d80cdR379
• https://github.com/walkor/workerman/pull/1150/changes#diff-f1e0bc96c431d22de194587082a047639ab3d2b4a26b62a8dee62ff7f86d80cdR390
• https://github.com/walkor/workerman/pull/1150/changes#diff-f1e0bc96c431d22de194587082a047639ab3d2b4a26b62a8dee62ff7f86d80cdR390
• https://github.com/walkor/workerman/pull/1150/changes#diff-f1e0bc96c431d22de194587082a047639ab3d2b4a26b62a8dee62ff7f86d80cdR398

A small discussion about the best way to do it will help.
For me the Http::encode() need to receive only string, even for Stringable. If any class have special code, it's OK but need to process the string to send it in the __to_string().