chore: bump version to 2.40.0

[dielduarte]

Bumps the version for the release that ships:

• Emails.metrics() (feat: add Emails.metrics() for account-level email metrics #262)
• broadcasts.recipients() (feat: add broadcasts.recipients() method #261)
• broadcasts.clicked_links() (feat: add broadcasts.clicked_links() method #263)
• fix: take the broadcast id as a positional argument in recipients (fix: take the broadcast id as a positional argument in recipients #264)

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Summary by cubic

Bumps the library version to 2.40.0 to publish new Email and Broadcast APIs and a recipients signature fix. Old: broadcasts.recipients required a keyword broadcast_id. New: it takes the broadcast id as the first positional argument.

• Adds Emails.metrics(), broadcasts.recipients(), and broadcasts.clicked_links().
• Migration: update calls to broadcasts.recipients(broadcast_id=...) to broadcasts.recipients(broadcast_id, ...).

^{Written for commit 797abf7. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

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

<sub>Requires human review: This version bump triggers a release containing public API changes and signature modifications that require human validation of the impact and versioning.

Re-trigger cubic</sub>