[FSSDK-11446] update: experiment_id and variation_id added to notification listener payloads

[FarhanAnjum-opti]

Summary

• Added experiment_id and variation_id to the decision notification listener payload in the Python SDK.
• Ensured that these IDs are included in all decision notifications sent via the notification center.
• Updated unit tests to validate the presence of experiment_id and variation_id in the payload.

Why

To support data warehouse-native customers who rely on SDK notification listeners to send experiment data to their data warehouse, we need to include experiment_id and variation_id in the payload. This ensures that the stats engine can correctly compute experiment results based on warehouse data.

Test Plan

• Modify existing or add unit tests to check for the presence of experiment_id and variation_id in the notification payload.
• Run all tests to confirm that the changes do not introduce regressions.

Issues

• FSSDK-11446

[coveralls]

coverage: 80.74% (+0.03%) from 80.714%
when pulling e2cfa9a on farhan-anjum/FSSDK-11446-add-exp/var-id-to-notif-listener
into 0237be2 on master.