Remove duo_workflow_compress_checkpoint feature flag

Summary

This issue tracks the removal of the duo_workflow_compress_checkpoint feature flag after successful rollout.

Feature

This feature flag controls whether the checkpoint payload between Duo Workflow Service and GitLab monolith is compressed using zlib and encoded using base64 to decrease payload size.

The feature has been successfully rolled out and enabled globally on GitLab.com.

Owners

• Team: Agent Foundations
• Most appropriate slack channel to reach out to: #g_agent_foundations
• Best individual to reach out to: @a_akgun

Steps

• Verify feature flag has been enabled in production for sufficient time (minimum 2 weeks)
• Confirm no issues reported related to compression
• Remove feature flag from codebase
• Update any related documentation
• Announce removal on #g_agent_foundations

Related

• Rollout issue: #577674