move nostr-sdk repository into here because why not?

sdk/cache/interface.go

@@ -0,0 +1,10 @@
+package cache
+
+import "time"
+
+type Cache32[V any] interface {
+	Get(k string) (v V, ok bool)
+	Delete(k string)
+	Set(k string, v V) bool
+	SetWithTTL(k string, v V, d time.Duration) bool
+}