feat(lib): add log filtering rules

Closes #942

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/logging/stdlib.go

@@ -0,0 +1,36 @@
+package logging
+
+import (
+	"bytes"
+	"context"
+	"log"
+	"log/slog"
+	"time"
+)
+
+// handlerWriter is an io.Writer that calls a Handler.
+// It is used to link the default log.Logger to the default slog.Logger.
+//
+// Adapted from https://cs.opensource.google/go/go/+/refs/tags/go1.24.5:src/log/slog/logger.go;l=62
+type handlerWriter struct {
+	h     slog.Handler
+	level slog.Leveler
+}
+
+func (w *handlerWriter) Write(buf []byte) (int, error) {
+	level := w.level.Level()
+	if !w.h.Enabled(context.Background(), level) {
+		return 0, nil
+	}
+	var pc uintptr
+
+	// Remove final newline.
+	origLen := len(buf) // Report that the entire buf was written.
+	buf = bytes.TrimSuffix(buf, []byte{'\n'})
+	r := slog.NewRecord(time.Now(), level, string(buf), pc)
+	return origLen, w.h.Handle(context.Background(), r)
+}
+
+func StdlibLogger(next slog.Handler, level slog.Level) *log.Logger {
+	return log.New(&handlerWriter{h: next, level: level}, "", log.LstdFlags)
+}