feat(automations): duplicate endpoint

[gabrielmfern]

Adds resend.Automations.duplicate(automation_id) and duplicate_async(automation_id) for POST /automations/{id}/duplicate.

Resolves DEV-1708. Mirrors the existing stop/stop_async pattern and resend-node resend/resend-node#1071.

🤖 Generated with Claude Code

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Summary by cubic

Adds resend.Automations.duplicate() and duplicate_async() to clone an automation via POST /automations/{id}/duplicate. Previously the SDK had no duplication method; now both sync and async clients can duplicate by ID without breaking existing behavior.

Review notes

• Adds Automations.DuplicateResponse with object and id for the new automation.
• Implements resend.Automations.duplicate(automation_id) and resend.Automations.duplicate_async(automation_id) using a POST to /automations/{id}/duplicate, mirroring the existing stop/stop_async pattern.
• Tests cover sync and async success paths and raise NoContentError when the API returns no body, consistent with existing error handling.
• Supports Linear DEV-1708 by exposing duplication in the Python SDK for Devtools usage.

^{Written for commit fa2baed. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

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

<sub>Auto-approved: Adds new duplicate/duplicate_async SDK methods for an existing endpoint, mirroring the established stop/stop_async pattern; tests cover success and error paths, and no existing behavior or contracts change.

Re-trigger cubic</sub>

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