fix: include custom metrics in cog predict --json output

[markphelps]

The Go Response struct was missing a Metrics field, causing json.Decoder to silently discard custom metrics from the coglet HTTP response. Add the field and an integration test that exercises the full CLI path (record_metric -> coglet -> Go CLI -> JSON output).

[ask-bonk]

Now I understand the full picture. The PR adds:

1. Metrics field to Response struct - This fixes the bug where custom metrics were being silently dropped during JSON decoding
2. Bonus improvements to GetSchema() - Better context handling and fixes a resource leak by adding defer resp.Body.Close()
3. Integration test - Verifies the end-to-end flow works correctly

All changes look correct:

• The omitempty tag maintains backward compatibility
• map[string]any is appropriate for arbitrary metrics
• The test exercises the full path from record_metric() → coglet → Go CLI → JSON output
• Resource leak in GetSchema() is fixed

LGTM

github run

[ask-bonk]

LGTM

github run