Switch PluginFrontend to domain sockets on macOS

[bell-db]

What changes are proposed in this pull request?

Fixes #379 by switching from TCP sockets to Unix domain sockets with server-side read timeout on macOS.

It turns out extremely difficult to find a reliable way to IPC on macOS, when the client is a simple bash script without accessing to mature frameworks. None of the above survived a stress test of 100k runs of 100KB messages:

• Named pipes get stuck: PosixPluginFrontend occasionally get stuck on macOS #366
• TCP sockets have port conflicts: Sockets aren't 100% reliable on macOS #379
• Domain sockets get stuck: Sockets aren't 100% reliable on macOS #379

However, when trying to implement a retry-on-timeout, it's found that, mysteriously, domain sockets with junixsocket server are working well with a server-side read timeout alone, even if we don't catch and retry (i.e. there is no timeout exception thrown or hang anymore). It's also the most performant solution on macOS:

Implementation	OS [1]	Short Message Roundtrip Latency (ms)	100KB Message Roundtrip Latency (ms)	Known issues
Named pipe	macOS	31.13	33.31	Missing EOF. Out of 100k runs: 70 timeouts
TCP socket (Java applet client)	macOS	80	83	Port conflict. Out of 100k runs: 10 timeouts, 26 empty responses, 8 Bad Request
TCP socket (netcat client)	macOS	16.06	17.77	Port conflict. Out of 100k runs: 8 timeouts, 20 empty responses, 4 Bad Request
Domain socket (netcat client)	macOS	14.64	16.28	nc with domain sockets / junixsocket missing EOF (w/o server read timeout). Out of 100k runs: 2.5k timeouts
Domain socket (nmap ncat client)	macOS		30.7	junixsocket missing EOF (w/o server read timeout)
Domain socket (socat client)	macOS		20.1	junixsocket missing EOF (w/o server read timeout)
Domain socket (Perl client)	macOS	24.94	25.52	junixsocket missing EOF (w/o server read timeout)
File + signal	macOS	27.65	29.80	Signal conflict when multiple generators
Named pipe	Linux	3.74	5.90	None (Passed 100k runs)
TCP socket (Java applet client)	Linux	3.96	5.63	None (Passed 100k runs)
TCP socket (netcat client)	Linux	1.82	3.67	None (Passed 100k runs)
Domain socket (netcat client)	Linux	1.83	3.59	None (Passed 100k runs)
File + signal	Linux	45.13	48.27	Signal conflict when multiple generators

[1]
macOS: macOS 14.6.1, M2 Max
Linux: Ubuntu 20.04.6 LTS, Xeon(R) Platinum 8375C

How is this tested?

Passes the stress test in #382, after adding client.setSoTimeout(60000).