fix(emoji): render a standard emoji for the reaction endpoints

[mikield]

EmojiBuilder::__toString() renders a standard emoji held under name as:

✅:

— the name, a colon, and an id that is not there. Every reaction on a standard emoji is a malformed request, and PHP warns about the undefined key on the way out.

public function __toString(): string
{
    return isset($this->data['name'])
        ? $this->data['name'] . ':' . $this->data['id']   // ← id may not exist
        : urlencode($this->data['id']);
}

The two halves of the library disagree about where a standard emoji lives. fromPart() copies name and skips id, because that is what Discord sends in a reaction event — so a builder made from a real event is exactly the case that cannot be rendered. The existing test wrote the emoji into setId() instead, which takes the other branch, which is why this held.

Both shapes work now, and the pair is what marks a custom emoji:

name	id	renders as
apex	12345	apex:12345
✅	—	%E2%9C%85
—	✅	%E2%9C%85

Found while porting a bot that votes on petitions with ✅ and ❌ reactions.

🤖 Generated with Claude Code

[github-actions]

🎉 This PR is included in version 1.3.2 🎉

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