feat: add subscriptions and rework interfaces

pkg/locker/locker.go

@@ -1,6 +1,9 @@
 package locker
 
-import "context"
+import (
+	"context"
+	"log"
+)
 
 type Locked[T any] struct {
 	state chan *T
@@ -23,6 +26,9 @@ func (s *Locked[T]) Modify(ctx context.Context, fn func(*T) error) error {
 	select {
 	case state := <-s.state:
 		defer func() { s.state <- state }()
+		log.Printf("locker %T to %p", state, fn)
+		defer log.Printf("locker %T from %p", state, fn)
+
 		return fn(state)
 	case <-ctx.Done():
 		return ctx.Err()