use batch IO when send to syslog and statsd

[zh-jq]

The IO code below:
syslog:

g3/lib/g3-syslog/src/async_streamer.rs

Line 159 in 6d0cbcf

fn send_data(&self, data: String, backend: &mut SyslogBackend) -> io::Result<()> {

statsd:

g3/lib/g3-statsd-client/src/sink/mod.rs

Line 126 in 6d0cbcf

self.io.send_msg(&self.buf)?;

should be updated to do batch IO send, we have done this for udpdump

g3/lib/g3-udpdump/src/stream/sink.rs

Line 57 in 6d0cbcf

async fn send_udp(&self, packets: &[Vec<u8>]) -> io::Result<()> {