Expose request builder methods

[GALCF]

Description

The audio request now exposes its toTextToSpeechRequest and toSpeechToTextRequest methods.

This can be useful for example if you have to preprocess request data in a configurator.

Example code:

<?php

protected function preprocessAudio(): void
{
    try {
        $audio = $this->request->toSpeechToTextRequest()->input();
    } catch (InvalidArgumentException) {
        // Is not a speech-to-text request
        return;
    }

    if (!$audio->hasRawContent()) {
        // Does not have readable content
        return;
    }

    $mimeType = $audio->mimeType();
    $content  = $audio->rawContent();
    Assert::notNull($content);

    // Preprocess $content here

    $audio = Audio::fromRawContent($content, $mimeType);

    $this->request->withInput($audio);
}