feat(Io.net): add allow_broadcast to BindOptions

* and implement it in `Threaded`, `Uring` and `Kqueue`

lib/std/Io/Kqueue.zig

@@ -1029,6 +1029,7 @@ fn netBindIp(
     var storage: Io.Threaded.PosixAddress = undefined;
     var addr_len = Io.Threaded.addressToPosix(address, &storage);
     try posixBind(k, socket_fd, &storage.any, addr_len);
+    if (options.allow_broadcast) try setSocketOption(k, socket_fd, posix.SOL.SOCKET, posix.SO.BROADCAST, 1);
     try posixGetSockName(k, socket_fd, &storage.any, &addr_len);
     return .{ .handle = socket_fd, .address = Io.Threaded.addressFromPosix(&storage) };
 }

lib/std/Io/Threaded.zig

@@ -12196,6 +12196,7 @@ fn netBindIpPosix(
     var storage: PosixAddress = undefined;
     var addr_len = addressToPosix(address, &storage);
     try posixBind(socket_fd, &storage.any, addr_len);
+    if (options.allow_broadcast) try setSocketOptionPosix(socket_fd, std.posix.SOL.SOCKET, std.posix.SO.BROADCAST, 1);
     try posixGetSockName(socket_fd, &storage.any, &addr_len);
     return .{ .handle = socket_fd, .address = addressFromPosix(&storage) };
 }
@@ -12212,6 +12213,7 @@ fn netBindIpWindows(
     const socket_handle = try openSocketAfd(family, options);
     errdefer windows.CloseHandle(socket_handle);
     const bound_address = try bindSocketIpAfd(socket_handle, address, .Active);
+    if (options.allow_broadcast) try setSocketOptionAfd(socket_handle, ws2_32.SOL.SOCKET, ws2_32.SO.BROADCAST, true);
     return .{ .handle = socket_handle, .address = bound_address };
 }
 

lib/std/Io/Uring.zig

@@ -4991,6 +4991,7 @@ fn netBindIp(
     var storage: PosixAddress = undefined;
     var addr_len = addressToPosix(address, &storage);
     try ev.bind(&maybe_sync.cancel_region, socket_fd, &storage.any, addr_len);
+    if (options.allow_broadcast) try ev.setsockopt(&maybe_sync.cancel_region, socket_fd, linux.SOL.SOCKET, linux.SO.BROADCAST, 1);
     try ev.getsockname(try maybe_sync.enterSync(ev), socket_fd, &storage.any, &addr_len);
     return .{ .handle = socket_fd, .address = addressFromPosix(&storage) };
 }

lib/std/Io/net.zig

@@ -282,6 +282,10 @@ pub const IpAddress = union(enum) {
         /// In this case, an IPv4 and an IPv6 application can bind to a single port
         /// at the same time.
         ip6_only: bool = false,
+        /// Allow the socket to send datagrams to broadcast addresses.
+        /// When not enabled any attempt to send datagrams to a broadcast address
+        /// will fail with `error.AccessDenied`
+        allow_broadcast: bool = false,
         mode: Socket.Mode,
         protocol: ?Protocol = null,
     };