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/kind_test.go

@@ -0,0 +1,37 @@
+package kind
+
+import (
+	"testing"
+
+	"lol.mleku.dev/chk"
+
+	"lukechampine.com/frand"
+)
+
+func TestMarshalUnmarshal(t *testing.T) {
+	var err error
+	k := make([]*K, 1000000)
+	for i := range k {
+		k[i] = New(uint16(frand.Intn(65535)))
+	}
+	mk := make([][]byte, len(k))
+	for i := range mk {
+		mk[i] = make([]byte, 0, 5) // 16 bits max 65535 = 5 characters
+	}
+	for i := range k {
+		mk[i] = k[i].Marshal(mk[i])
+	}
+	k2 := make([]*K, len(k))
+	for i := range k2 {
+		k2[i] = New(0)
+	}
+	for i := range k2 {
+		var r []byte
+		if r, err = k2[i].Unmarshal(mk[i]); chk.E(err) {
+			t.Fatal(err)
+		}
+		if len(r) != 0 {
+			t.Fatalf("remainder after unmarshal: '%s'", r)
+		}
+	}
+}