feat: add broadcasts.recipients() method

[dielduarte]

Adds Broadcasts.recipients() / recipients_async() for GET /broadcasts/{id}/recipients.

Spec: resend/resend-openapi#97
Node reference: resend/resend-node#1078

Tests: 584 passed. flake8 + mypy clean.

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Summary by cubic

Adds resend.Broadcasts.recipients() and resend.Broadcasts.recipients_async() to list a broadcast’s recipients by event type with filters and cursor pagination. Previously recipient-level delivery and engagement data was not available; now clients can query sent, delivered, opened, clicked, bounced, and more, with counts and clicked links when applicable.

• Public API: exports RecipientsParams, RecipientsResponse, BroadcastRecipient, BroadcastRecipientEventType, BroadcastRecipientBounceType, and BroadcastRecipientClickedLink via resend.__init__.
• Request: requires broadcast_id (path) and type; optional email, bounce_type (only with type="bounced"), limit (1–100), and cursor params after/before (mutually exclusive).
• Response: returns object="list", data: List[BroadcastRecipient], has_more; optional count for opened/clicked, bounce_type for bounced, and clicked_links for clicked.
• Errors and examples: raises ResendError on 404 and NoContentError on empty responses; adds sync/async examples and tests covering success, pagination, optional fields, and error cases.

^{Written for commit 7a29780. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 7 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Requires human review: Adds new recipients and recipients_async methods to the Broadcasts module, along with supporting data models and tests for the new API endpoint.

Re-trigger cubic</sub>