Chore: simplify build infra

Build/lib/is-fast-ip.ts

@@ -31,3 +31,47 @@ export function isProbablyIpv4(hostname: string): boolean {
     && /* '.' */ hostname.charCodeAt(hostname.length - 1) !== 46 /* '.' */
   );
 }
+
+export function isProbablyIpv6(hostname: string): boolean {
+  if (hostname.length < 3) {
+    return false;
+  }
+
+  let start = hostname[0] === '[' ? 1 : 0;
+  let end = hostname.length;
+
+  if (hostname[end - 1] === ']') {
+    end -= 1;
+  }
+
+  // We only consider the maximum size of a normal IPV6. Note that this will
+  // fail on so-called "IPv4 mapped IPv6 addresses" but this is a corner-case
+  // and a proper validation library should be used for these.
+  if (end - start > 39) {
+    return false;
+  }
+
+  /* eslint-disable sukka/no-single-return -- here it goes */
+  let hasColon = false;
+
+  for (; start < end; start += 1) {
+    const code = hostname.charCodeAt(start);
+
+    if (code === 58 /* ':' */) {
+      hasColon = true;
+    } else if (
+      !(
+        (
+          (code >= 48 && code <= 57) // 0-9
+          || (code >= 97 && code <= 102) // a-f
+          || (code >= 65 && code <= 90) // A-F
+        )
+      )
+    ) {
+      return false;
+    }
+  }
+
+  return hasColon;
+  /* eslint-enable sukka/no-single-return -- here it goes */
+}