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

internal/requestlog/requestlog.go

@@ -1,6 +1,6 @@
 // Package requestlog writes the lines smallwebwaf prints on stdout: one
-// JSON object per request, marked "type":"request", and the process's own
-// messages as JSON lines marked "type":"process".
+// JSON object per request, or two from servewaf, marked "type":"request", and
+// the process's own messages as JSON lines marked "type":"process".
 package requestlog
 
 import (
@@ -60,6 +60,16 @@ const OffenceLimit = "limit"
 // that broke the error burst.
 const LimitHitErrorBurst = "error_burst"
 
+// The servewaf_line a request line names, which says which of servewaf's two
+// lines about a question it is.
+const (
+	// ServeWAFLineDecision is servewaf's line at its decision.
+	ServeWAFLineDecision = "decision"
+	// ServeWAFLineReport is servewaf's line when rproxy's report comes, with
+	// the decision's fields and the report's together.
+	ServeWAFLineReport = "report"
+)
+
 // timeLayout is RFC 3339 with milliseconds.
 const timeLayout = "2006-01-02T15:04:05.000Z07:00"
 
@@ -70,6 +80,9 @@ const timeLayout = "2006-01-02T15:04:05.000Z07:00"
 //nolint:tagliatelle // docs/request-log.md names the fields in snake_case
 type Line struct {
 	Type string `json:"type"`
+	// ServeWAFLine is ServeWAFLineDecision or ServeWAFLineReport on servewaf's
+	// two lines about a question.
+	ServeWAFLine string `json:"servewaf_line,omitempty"`
 
 	// The standard web log fields. Scheme is how the client reached
 	// smallwebwaf, or the trusted proxy in front of it.