feat: add support for @sheepdog-transform comment

[paoloricciuti]

Just had an awesome idea on lunch and couldn't restrain myself from implementing it. With this change users will have the ability to annotate a function so that it can be converted by the async transform. This means that even if they don't want to write the task inline for some reason they can just do

/**
 * @sheepdog-transform
 */
export async function task_fn() {
    await Promise.resolve();
}

and the vite plugin will convert this into

/**
 * @sheepdog-transform
 */
export async function* task_fn() {
    yield Promise.resolve();
}

I had to change some test because now we are keeping comments but that's it. WDYT about this feature? If we are ok with it i'll add this to the documentation.

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[marcoow]

would a decorator not be better than a magic comment?

[paoloricciuti]

would a decorator not be better than a magic comment?

Decorators are only available for classes tho, you need to import them and this is actually not something we do at runtime but at build time so if we use the decorator would actually just be an "identity decorator" that just returns the function as is