use recycler for packetbatch allocation

[lijunwangs]

Problem

It is found that the packet coalescer packet_batch_sender in quic streamer is lagging behind the streamer's ingestion of packets under load testing. And one of the costly operations are malloc for new PacketBatch.

Summary of Changes

Use PacketBatchRecycler to reduce the malloc cost.

Fixes #

[lijunwangs]

CPU usage for the coalescer without the recycler:

With the recycler:

[behzadnouri]

lgtm, but I would suggest to also confirm that the runtime performance improves in terms of some timing, throughput or latency metrics, etc. (perf profiles can sometimes be misleading and inconsistent with metrics).

[lijunwangs]

In my test configurations using bench-vote tool, with everything else equal, with two sender clients:

I got the following sustained rates from the sink: (reported every 5 s)

With fix:
Received txns count: 2740424

Vs without:

Received txns count: 1402725