backend, net: optimize read/write connection by forwarding packets

[djshow832]

What problem does this PR solve?

Issue Number: close #381

Problem Summary:
The performance is still not good enough. We can just forward the packets between connections and avoid allocating memory and copying data.

What is changed and how it works:

• Add PacketIO.ForwardUntil and call it in CmdProcessor.forwardUntilResultEnd. ForwardUntil only allocates memory in the last packet. ForwardUntil mainly calls Writer.ReadFrom to copy data between reader and writer.
• Copy Golang bufio.go to TiProxy because Writer.ReadFrom always calls TCPConn.ReadFrom, which calls sys calls and skips the buffer. We always need the buffer and I can't find a replacement of bufio.
• Add ReadFrom for all the packetReadWriter implementations.
• Modify the parameters of IsXXXPacket because we only know the length and first byte if we do the optimization.
• Optimize compressedReadWriter.Peek to avoid allocating memory.
• Add proxyReadWriter.Peek. It was a bug not to add this function.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Sysbench Result

Before this PR (with conn-buffer-size=131072):

Range size	QPS	TiProxy CPU	QPS per 100% CPU
10	32818	150%	21878
100	22392	190%	11785
1000	4093	200%	2046
10000	449	200%	224

After this PR (with conn-buffer-size=131072):

Range size	QPS	TiProxy CPU	QPS per 100% CPU
10	31430	130%	24176
100	23680	150%	15786
1000	6281	160%	3925
10000	707	140%	505

Flame Graph

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xhebox

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-02 03:25:31.109708043 +0000 UTC m=+3096328.696818187: ☑️ agreed by xhebox.