feat(broadcasts): add duplicate endpoint

[gabrielmfern]

Ports resend.broadcasts.duplicate(id) from the Node SDK: Broadcasts.duplicate(String id) posts to /broadcasts/{id}/duplicate, the endpoint added in resend/resend-openapi#115, and returns a DuplicateBroadcastResponseSuccess carrying the id of the new draft. The method matches Templates.duplicate and Automations.duplicate; the response type follows the broadcasts package and extends BaseBroadcastResponse like CancelBroadcastResponseSuccess instead of being a flat DTO like theirs. The release carries 4.25.0.

Staging call through Broadcasts.duplicate from the 4.25.0 jar in Maven local. HttpClient.BASE_API is a hardcoded constant, so the call went through a HttpClient subclass with perform overridden to hit https://api.resend-staging.com; the copy was deleted afterwards.

source id: e6bd3843-3cc7-4c0d-b7fd-e01cbb514a16
getObject(): broadcast
getId():     8adc9b5a-65ff-43c5-b0b5-f4517912927f
id differs from source: true

Left open on purpose: object is now duplicated across CancelBroadcastResponseSuccess, RemoveBroadcastResponseSuccess, and DuplicateBroadcastResponseSuccess and could be hoisted into BaseBroadcastResponse. That touches the sibling models, so it stays out of this single-endpoint port.

🤖 Generated with Claude Code

---

Summary by cubic

Adds Broadcasts.duplicate(id) to the Java SDK, matching the Node SDK's resend.broadcasts.duplicate and the endpoint from resend/resend-openapi#115.

The new method posts to /broadcasts/{id}/duplicate and returns a DuplicateBroadcastResponseSuccess with the new draft's ID. The version bumps to 4.25.0.

Refactors

• object is now duplicated across CancelBroadcastResponseSuccess, RemoveBroadcastResponseSuccess, and DuplicateBroadcastResponseSuccess; hoisting it into BaseBroadcastResponse is left for a future PR to keep this change focused.

^{Written for commit 291c2f1. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 4 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>