servewaf answers rproxy's question about each request and takes its report (closes #170)

`smallwebwaf servewaf` runs today's checks on the visitor's request each
question carries, answers rproxy, and passes nothing to an app. rproxy reports
every request servewaf answered. A report counts an allowed request's bytes and
writes servewaf's second log line. The table holds a copy of what a report
needs, never the request, so a report cannot reach a request being handled.

Judgement call: a question's body is read before any check; over 64 KiB gets 400.
Judgement call: a report's bytes and durations have ceilings, so they cannot overflow.
Judgement call: a `close` disposition for SWWAF_BAN_RESPONSE=close.

Model: opus-5-5

cmd/smallwebwaf/main.go

@@ -1,6 +1,7 @@
 // Command smallwebwaf is a web application firewall for one app: it runs
-// between traefik and the app, and passes requests through within its
-// limits. Everything it does is in internal/smallwebwaf.
+// between traefik and the app and passes requests through within its limits,
+// or, as `smallwebwaf servewaf`, answers rproxy's questions about them.
+// Everything it does is in internal/smallwebwaf.
 package main
 
 import (