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/protocol/relayinfo/fetch.go

@@ -0,0 +1,48 @@
+package relayinfo
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"time"
+
+	"lol.mleku.dev/chk"
+	"lol.mleku.dev/errorf"
+	"next.orly.dev/pkg/utils/normalize"
+)
+
+// Fetch fetches the NIP-11 Info.
+func Fetch(c context.Context, u []byte) (info *T, err error) {
+	if _, ok := c.Deadline(); !ok {
+		// if no timeout is set, force it to 7 seconds
+		var cancel context.CancelFunc
+		c, cancel = context.WithTimeout(c, 7*time.Second)
+		defer cancel()
+	}
+	u = normalize.URL(u)
+	var req *http.Request
+	if req, err = http.NewRequestWithContext(
+		c, http.MethodGet, string(u), nil,
+	); chk.E(err) {
+		return
+	}
+	// add the NIP-11 header
+	req.Header.Add("Accept", "application/nostr+json")
+	// send the response
+	var resp *http.Response
+	if resp, err = http.DefaultClient.Do(req); chk.E(err) {
+		err = errorf.E("request failed: %w", err)
+		return
+	}
+	defer chk.E(resp.Body.Close())
+	var b []byte
+	if b, err = io.ReadAll(resp.Body); chk.E(err) {
+		return
+	}
+	info = &T{}
+	if err = json.Unmarshal(b, info); chk.E(err) {
+		return
+	}
+	return
+}