feat: add broadcasts.clickedLinks() endpoint

[dielduarte]

Adds GET /broadcasts/{id}/clicked-links — paginated list of a broadcast's clicked links (url, clicks, unique_clicks).

Spec: resend/resend-openapi#95
Reference implementation: resend/resend-node#1077

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Summary by cubic

Adds GET /broadcasts/{id}/clicked-links and $client->broadcasts->clickedLinks->list() to fetch a broadcast’s clicked URLs with total and unique click counts. Previously the SDK had no way to retrieve link click stats for broadcasts; this enables paginated reporting without breaking existing behavior.

• Introduces Resend\Broadcasts\ClickedLink resource and registers the 'broadcast-clicked-links' mapping in Service for collection hydration.
• Adds Resend\Service\Broadcasts\ClickedLink::list(string $broadcastId, array $options = []) supporting limit, before, and after.
• Populates Broadcast::$clickedLinks by constructing the service in Broadcast::__construct.
• Returns Collection<Resend\Broadcasts\ClickedLink> where id is an opaque pagination cursor; do not treat it as an entity identifier.
• Tests cover basic listing and pagination; no migrations or breaking changes.

^{Written for commit b945ef3. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 6 files

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