feat: Add delete graph with immediate and period-end cancellation options

[jfrench9]

Summary

Implements enhanced delete graph functionality that supports both immediate deletion and period-end cancellation options. This includes a new subscription cancellation API, updated graph client methods, and corresponding model changes to support the two deletion modes.

Key Accomplishments

• New Subscription Cancellation API: Added cancel_repository_subscription.py module that handles cancelling repository subscriptions, enabling period-end cancellation flows where a graph's associated subscription can be terminated at the end of the current billing period rather than immediately.

• Enhanced Delete Graph Operation: Refactored op_delete_graph.py to support both immediate deletion and period-end deletion strategies. The operation now accommodates different cancellation semantics depending on the user's intent.

• Updated Graph Client: Extended graph_client.py with new methods and logic to orchestrate the delete graph workflow, integrating the subscription cancellation step when period-end deletion is selected.

• Updated Data Models: Modified delete_graph_op.py models to include fields and structures necessary to distinguish between immediate and period-end deletion modes.

• Test Coverage: Added tests in test_graph_client.py to validate the new delete graph functionality across both deletion options.

Breaking Changes

• The delete graph operation interface has been modified with new parameters/options. Existing callers that invoke the delete graph operation may need to be updated to specify the desired deletion mode (immediate vs. period-end).
• Model changes in delete_graph_op.py may affect serialization/deserialization for consumers relying on the previous schema.

Testing Notes

• New unit tests cover the delete graph flow for both immediate and period-end cancellation scenarios.
• Verify integration behavior with the subscription cancellation endpoint to ensure period-end cancellations are correctly propagated to the billing system.
• Edge cases to validate: deleting a graph with no active subscription, attempting period-end cancellation on an already-cancelled subscription, and concurrent deletion requests.

Infrastructure Considerations

• The new subscription cancellation endpoint must be available and properly configured in the target environment before deploying this change.
• Ensure API permissions and authentication scopes cover the new subscription cancellation operations.
• Monitor billing and subscription service logs during rollout to confirm cancellation requests are processed correctly.

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Branch Info:

• Source: chore/update-cancel-repo-sub
• Target: main
• Type: feature

Co-Authored-By: Claude noreply@anthropic.com