perf: non-blocking sockets

[olavloite]

Switch from blocking to non-blocking sockets. This reduces latency in low QPS use cases.

[codecov]

Codecov Report

Attention: Patch coverage is 84.69388% with 60 lines in your changes are missing coverage. Please review.

Project coverage is 90.09%. Comparing base (eb822d8) to head (d65455a).
Report is 4 commits behind head on postgresql-dialect.

Files	Patch %	Lines
...loud/spanner/pgadapter/NonBlockingProxyServer.java	80.82%	10 Missing and 4 partials ⚠️
...oud/spanner/pgadapter/NonBlockingSocketReader.java	91.80%	6 Missing and 4 partials ⚠️
...panner/pgadapter/NonBlockingConnectionHandler.java	80.95%	7 Missing and 1 partial ⚠️
...panner/pgadapter/metadata/ChannelOutputStream.java	58.82%	5 Missing and 2 partials ⚠️
...d/spanner/pgadapter/NonBlockingServerListener.java	89.58%	3 Missing and 2 partials ⚠️
...nner/pgadapter/metadata/ByteBufferInputStream.java	54.54%	4 Missing and 1 partial ⚠️
...nner/pgadapter/metadata/ForwardingInputStream.java	44.44%	4 Missing and 1 partial ⚠️
...spanner/pgadapter/wireprotocol/ControlMessage.java	55.55%	3 Missing and 1 partial ⚠️
...ava/com/google/cloud/spanner/pgadapter/Server.java	0.00%	1 Missing ⚠️
...apter/statements/ExtendedQueryProtocolHandler.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##             postgresql-dialect    #1562      +/-   ##
========================================================
- Coverage                 90.87%   90.09%   -0.78%     
- Complexity                 2705     2769      +64     
========================================================
  Files                       144      151       +7     
  Lines                      9257     9592     +335     
  Branches                   1345     1383      +38     
========================================================
+ Hits                       8412     8642     +230     
- Misses                      568      653      +85     
- Partials                    277      297      +20     

Flag	Coverage Δ
all_tests	90.09% <84.69%> (-0.78%)	⬇️

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