…nges

Add a polling goroutine that refreshes agentFeatures from the Datadog Agent's
/info endpoint every 5 seconds (overridable in tests via config). Dynamic
fields (DropP0s, Stats, peerTags, spanEventsAvailable, obfuscationVersion) are
updated from each successful response. Static fields that are baked into
transport, stats, and appsec components at startup (v1ProtocolAvailable,
StatsdPort, evpProxyV2, metaStructAvailable, featureFlags, defaultEnv) are
always preserved from the startup snapshot.

When a poll fails the last-known-good snapshot is retained. The goroutine exits
cleanly when the tracer is stopped via the existing t.stop channel.

Add table-driven tests covering: static-field preservation, dynamic updates,
error resilience, and goroutine shutdown.

- Add CAS-loop update() to atomicAgentFeatures to prevent potential
  load-modify-store races if refreshAgentFeatures is ever called
  concurrently in the future
- Add errAgentFeaturesNotSupported sentinel for 404 responses so both
  startup and polling callers uniformly treat 404 as "keep last good"
  without zeroing dynamic fields
- Bound HTTP response body with io.LimitReader(1 MiB) before JSON decode
  to prevent DoS from a misbehaving agent
- Use agentURL.JoinPath("info") instead of fmt.Sprintf for safe URL
  construction
- Add agentEnabled() helper on config to consolidate the three-part
  condition for launching the poll goroutine, replacing the inline copy
- Fix comment typo: agentInfoPollInterval → defaultAgentInfoPollInterval
- Use maps.Clone for featureFlags in refreshAgentFeatures for defensive
  isolation between snapshots
- Import errors and maps in tracer.go
- Test: add Stats to dynamic-field assertions in
  TestRefreshAgentFeaturesPreservesStaticFields
- Test: add TestPollAgentInfoRetainsLastKnownGoodOn404
- Test: use any instead of interface{} in handlers; add error handling
  for json.NewEncoder().Encode(); remove time.Sleep from goroutine-stop
  test (unnecessary)

- refreshAgentFeatures: use local copy f := newFeatures in the update()
  closure so CAS retries always start from the original fetched state
  (pure-transform contract required by the CAS loop)
- refreshAgentFeatures: clone peerTags slice alongside featureFlags map to
  prevent the new snapshot from aliasing the old one's backing array
- fetchAgentFeatures: return a clear error for non-200/non-404 HTTP status
  codes instead of falling through to JSON decode on 5xx responses
- TestPollAgentInfoUpdatesFeaturesDynamically: load agent snapshot once
  in the assert.Eventually predicate to avoid a TOCTOU double-load
- TestPollAgentInfoGoroutineStopsOnTracerStop: replace time.After with
  time.NewTimer + defer timer.Stop() to prevent timer resource leak
- TestPollAgentInfoRetainsLastKnownGoodOnError: add defer srv.Close()
  so the server is always reclaimed even on early test failure
- TestPollAgentInfoRetainsLastKnownGoodOn404: use w.WriteHeader instead
  of http.NotFound(w, nil) to avoid passing a nil *http.Request

Place "slices" after rt "runtime/trace" in alphabetical import order.
Remove extra alignment spaces before inline comments to satisfy gofmt.

…atures

Both fields are consumed only by startTelemetry(), which runs once at
startup and produces an immutable telemetry client. Updating them during
periodic /info polling would have no observable effect, so preserve their
startup values alongside the other static fields.

Also extends TestRefreshAgentFeaturesPreservesStaticFields to include
/telemetry/proxy/ in the startup endpoint list and assert that both
fields remain frozen across a manual refresh call.

- Use local af variable in newConfig to avoid redundant load() calls
- Change resolveDogstatsdAddr to take (addr string, af agentFeatures) instead of *config
- Extract pollAgentInfo method from inline goroutine in newTracer
- Add context.Context to fetchAgentFeatures; use NewRequestWithContext so in-flight /info requests cancel promptly on tracer shutdown
- Fix agentInfoPollInterval comment to drop file reference

- telemetry.go: hoist dual c.agent.load() calls to a single local var
  so DropP0s and StatsdPort come from the same atomic snapshot; removes
  the now-redundant second load() near the proxy check (same pattern
  as startTelemetry's existing usage at line 120).
- tracer.go: document that the bridging goroutine lifetime is bounded by
  defer cancel() so no WaitGroup tracking is needed.
- tracer.go: document that f is a shallow copy of newFeatures and that
  reference-typed fields must be cloned to avoid shared backing storage
  across CAS retries.
- option.go: drain the 404 response body before returning so the
  underlying HTTP connection can be reused (keep-alive).