Add first-party calculate latency and uptime analytics

[PavelMakarchuk]

Problem

The developer portal now has a live latency/uptime view, but its latency data is only partial. Today it comes from:

• the portal synthetic probe, fired every 5 minutes
• portal-originated Run traffic

That does not measure all real partner production /calculate traffic. The household API already records value-free calculate analytics with trusted client_id, status code, requested/resolved channel, model version, endpoint, method, and variable usage, but it does not store request duration.

Goal

Record first-party calculate request latency in policyengine-household-api so the portal can show true live latency and uptime for production partner API traffic.

Proposed work

• Add a duration_ms or equivalent integer column to calculate_requests via Alembic migration.
• Measure wall-clock request duration around the calculate handler in the analytics decorator.
• Persist duration for successful responses, error responses, and exceptions where analytics is enabled.
• Expose latency/uptime aggregations from the analytics API, either by extending /analytics/calculate/requests or adding a focused endpoint.
• Support filters needed by the portal:
  • time window / start and end time
  • resolved channel: current / frontier
  • optionally client_id for staff-only partner drilldown, once authorization rules are decided
• Return enough aggregate data for the portal to show p50, p95, p99, count, error count, and uptime by time bucket.

Acceptance criteria

• Real authenticated /calculate requests produce analytics rows with trusted client_id and duration_ms.
• Failed calculate requests and thrown exceptions record status/error state and duration where possible.
• Analytics endpoint can return bucketed latency and uptime for current/frontier over recent windows.
• No request bodies, response bodies, household values, entity IDs, or other sensitive values are logged.
• Unit tests cover migration/model changes, duration recording, exception paths, and analytics aggregation.
• Deployed analytics metadata test is updated or extended to assert duration is recorded.

Context

Portal PR: https://github.com/PolicyEngine/policyengine-developer-portal/pull/20

Current limitation in the portal: the dashboard is useful as an availability canary, but it is not yet true production partner latency because household API does not emit first-party latency metrics.