[Agent][Platform][OpenAI] Add stream usage support

[oesteve]

Q	A
Bug fix?	no
New feature?	yes
Docs?	no
Issues	Fix #753
License	MIT

$result = $agent->call($messages, [
    'stream' => true, // enable streaming of response text
    'stream_options' => [
        'include_usage' => true, // include usage in the response
    ],
]);

/** @var TextChunk $textChunk */
foreach ($result->getContent() as $textChunk) {
    // $textChunk implement \Stringable
    echo $textChunk->getContent();

    // Chunk also contain metadata
    // $textChunk->getMetadata()->get('id'); // Stream id
}

// Output token usage statistics for each call
foreach ($result->getMetadata()->get('calls', []) as $call) {
    echo \PHP_EOL.sprintf(
        '%s: %d tokens - Finish reason: [%s]',
        $call['id'],
        $call['usage']['total_tokens'],
        $call['finish_reason']
    );
}

[OskarStark]

remove?

[OskarStark]

remove

[OskarStark]

Suggested change

// Output text chunks