* claim: #6389
* perf: write each control reply to the socket in one piece
The control server wrote each reply with writeln!(out, "{reply}") on the unbuffered TcpStream.
Formatting a serde_json::Value hands the writer every string, number and punctuation mark
separately, so each became its own write system call. A reply of a few megabytes (component.list
on a design with thousands of components) took about half a second to send.
Every reply is now serialized to one buffer and written at once. Writing one large Value to a
loopback TcpStream: 1.79 MB took 1,052 ms with writeln! and 4.9 ms with one write_all.
The test counts the write calls for a 2000-component reply (one) and reads it back.
JK3D
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