refactor visitor IPs and allow exempting IP Ranges

Use netip.Addr instead of storing addresses as strings. This requires
conversions at the database level and in tests, but is more memory
efficient otherwise, and facilitates the following.

Parse rate limit exemptions as netip.Prefix. This allows storing IP
ranges in the exemption list. Regular IP addresses (entered explicitly
or resolved from hostnames) are IPV4/32, denoting a range of one
address.

util/util.go

@@ -5,8 +5,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"github.com/gabriel-vasile/mimetype"
-	"golang.org/x/term"
 	"io"
 	"math/rand"
 	"os"
@@ -15,6 +13,9 @@ import (
 	"strings"
 	"sync"
 	"time"
+
+	"github.com/gabriel-vasile/mimetype"
+	"golang.org/x/term"
 )
 
 const (
@@ -45,6 +46,16 @@ func Contains[T comparable](haystack []T, needle T) bool {
 	return false
 }
 
+// ContainsContains returns true if any element of haystack .Contains(needle).
+func ContainsContains[T interface{ Contains(U) bool }, U any](haystack []T, needle U) bool {
+	for _, s := range haystack {
+		if s.Contains(needle) {
+			return true
+		}
+	}
+	return false
+}
+
 // ContainsAll returns true if all needles are contained in haystack
 func ContainsAll[T comparable](haystack []T, needles []T) bool {
 	matches := 0