net, config: optimize read and write packets

[djshow832]

What problem does this PR solve?

Issue Number: close #381

Problem Summary:
WritePacket and ReadPacket become the hot path when there are many rows returned, so this code should be optimized:

• WriteOnePacket calls 2 NewReader and that allocates memory twice.
• ReadPacket grows slice in data = append(data, buf), which is unncessary.
• var header [4]byte escapes to the heap because header is passed as a parameter to other functions.
• The read/write buffer size is 16K, which means for 1000 rows, it calls syscall read/write 8 times.
• io.ReadFull contains unnecessary boundary checks, function calls, and interface conversion.

What is changed and how it works:
Optimization:

• Replace io.Copy with readWriter.Write to remove NewReader.
• Do not call data = append(data, buf) for the first packet.
• Move header into PacketIO/compressedReadWriter as a member.
• Make conn-buffer-size configurable and set to 32K by default. It can't be too large in case there are tens of thousands of idle connections.
• Replace io.ReadFull with customized ReadFull.

Others:

• Add DirectWrite to compressedReadWriter because it was missed, but it doesn't matter actually.
• Also add benchmarks of compression.

Check List

Tests

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

Benchmark Result

Before this PR:
BenchmarkWritePacket-8 2721517 607.5 ns/op 328 B/op 6 allocs/op
BenchmarkReadPacket-8 2829 413287 ns/op 2097727 B/op 6 allocs/op

After this PR:
BenchmarkWritePacket-8 10362842 116.3 ns/op 112 B/op 1 allocs/op
BenchmarkReadPacket-8 5344 232485 ns/op 1049217 B/op 1 allocs/op

Sysbench Result

Before this PR:

Range size	QPS	TiProxy CPU	QPS per 100% CPU
10	30955	180%	17200
100	14655	190%	7710
1000	2112	200%	1060
10000	221	200%	110

After 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

Flame Graph

Before this PR:

After this PR:

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:

• 2023-10-18 07:40:51.781857437 +0000 UTC m=+1815649.368967583: ☑️ agreed by xhebox.