feat(contacts): add segment_id support to Contacts.list

[drish]

Implements GET /segments/{segment_id}/contacts by adding an optional segment_id parameter to Contacts.list() and Contacts.list_async().

Closes #201

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Summary by cubic

Add support for listing contacts by segment using an optional segment_id in Contacts.list() and Contacts.list_async(). This calls GET /segments/{segment_id}/contacts and keeps global/audience listing (audience_id is now deprecated).

• New Features

  • Added segment_id to sync/async list methods to fetch segment contacts.
  • Automatically selects base path: /segments/{segment_id}/contacts, else /audiences/{audience_id}/contacts, else /contacts.

• Migration

  • Use segment_id for segment queries going forward; audience_id remains for backward compatibility but is deprecated.

^{Written for commit 3c7ac8a. 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.

_{Shadow auto-approve: would auto-approve. Additive feature adding optional segment_id support to contact listing with comprehensive tests. Low risk and follows existing SDK patterns.}