Add relayinfo package and utility modules for NIP-11 support

Introduce the `relayinfo` package with `NIP-11` utilities, including `Fees`, `Limits`, and `NIPs` structures. Add utility modules for handling numbers, timestamps, and kinds. Integrate functionality for fetching and managing relay information.

pkg/encoders/kind/kinds_test.go

@@ -0,0 +1,36 @@
+package kind
+
+import (
+	"testing"
+
+	"lol.mleku.dev/chk"
+	"lukechampine.com/frand"
+)
+
+func TestUnmarshalKindsArray(t *testing.T) {
+	k := &S{make([]*K, 100)}
+	for i := range k.K {
+		k.K[i] = New(uint16(frand.Intn(65535)))
+	}
+	var dst []byte
+	var err error
+	if dst = k.Marshal(dst); chk.E(err) {
+		t.Fatal(err)
+	}
+	k2 := &S{}
+	var rem []byte
+	if rem, err = k2.Unmarshal(dst); chk.E(err) {
+		return
+	}
+	if len(rem) > 0 {
+		t.Fatalf("failed to unmarshal, remnant afterwards '%s'", rem)
+	}
+	for i := range k.K {
+		if *k.K[i] != *k2.K[i] {
+			t.Fatalf(
+				"failed to unmarshal at element %d; got %x, expected %x",
+				i, k.K[i], k2.K[i],
+			)
+		}
+	}
+}