Fix Polymarket client pacing

[novatechflow]

Summary

• pace positions, activity, and P/L independently
• stagger shared Data API calls and add jittered exponential backoff
• honor Retry-After while retaining cached dashboard data
• align P/L polling with its 30-minute cache window

Validation

• go test ./...
• go test -race ./...
• go test -count=20 ./...
• go vet ./...
• go build -o /tmp/polydisplayd-pacing .
• git diff --check