Read SWWAF_IPV6_GROUP_PREFIX, SWWAF_MAX_TRACKED_CLIENTS and SWWAF_LOG_LEVEL (closes #112)

The IPv6 group that is one client, the size of the table of clients and
the level of the process's own lines become settings. clientGroup reads
the group length from them, so limits, bans, history, lookups, AbuseIPDB
scores and per-client anomaly counters all follow it; ratelimit.New
takes the table size; the process logger takes the level once the
settings are read, and request lines, written apart from it, are never
held back.

Judgement call: SWWAF_IPV6_GROUP_PREFIX accepts 32 to 128, the issue's example range.

Model: opus-5-5

internal/requestlog/requestlog.go

@@ -193,8 +193,11 @@ func Milliseconds(d time.Duration) float64 {
 // NewProcessLogger returns the logger for the process's own messages:
 // JSON lines on w, marked "type":"process", with the time in the same form
 // as a request line's, and instanceName, SWWAF_INSTANCE_NAME, as instance.
-func NewProcessLogger(w io.Writer, instanceName string) *slog.Logger {
+// It writes only the messages at level, SWWAF_LOG_LEVEL, or more severe;
+// the request lines Write writes are never held back.
+func NewProcessLogger(w io.Writer, instanceName string, level slog.Level) *slog.Logger {
 	handler := slog.NewJSONHandler(w, &slog.HandlerOptions{
+		Level: level,
 		ReplaceAttr: func(groups []string, attr slog.Attr) slog.Attr {
 			if attr.Key == slog.TimeKey && len(groups) == 0 {
 				return slog.String(slog.TimeKey, FormatTime(attr.Value.Time()))