fix: cancel requests were ignored

[olavloite]

Cancel requests for a (long-running) query or other statement was ignored by PGAdapter. This fix makes sure that both long-running queries, updates and COPY operations can be cancelled.

Fixes b/245128300

[codecov]

Codecov Report

Merging #356 (9ce10ec) into postgresql-dialect (afcd59e) will increase coverage by 0.00%.
The diff coverage is 61.81%.

@@                  Coverage Diff                  @@
##             postgresql-dialect     #356   +/-   ##
=====================================================
  Coverage                 86.39%   86.40%           
- Complexity                 1822     1828    +6     
=====================================================
  Files                       121      121           
  Lines                      6004     6023   +19     
  Branches                    823      826    +3     
=====================================================
+ Hits                       5187     5204   +17     
  Misses                      590      590           
- Partials                    227      229    +2     

Flag	Coverage Δ
all_tests	86.40% <61.81%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...loud/spanner/pgadapter/statements/DdlExecutor.java	91.27% <0.00%> (ø)
...apter/statements/ExtendedQueryProtocolHandler.java	93.02% <0.00%> (-4.54%)	⬇️
...er/pgadapter/statements/IntermediateStatement.java	93.33% <0.00%> (-3.22%)	⬇️
.../cloud/spanner/pgadapter/utils/MutationWriter.java	90.24% <0.00%> (-1.35%)	⬇️
...spanner/pgadapter/wireprotocol/ControlMessage.java	86.63% <0.00%> (-0.87%)	⬇️
...panner/pgadapter/wireprotocol/DescribeMessage.java	85.71% <0.00%> (ø)
...panner/pgadapter/statements/BackendConnection.java	90.71% <40.00%> (-0.19%)	⬇️
...loud/spanner/pgadapter/utils/CopyDataReceiver.java	94.11% <50.00%> (-5.89%)	⬇️
...gle/cloud/spanner/pgadapter/ConnectionHandler.java	86.94% <88.88%> (+2.95%)	⬆️
...ud/spanner/pgadapter/error/PGExceptionFactory.java	100.00% <100.00%> (ø)
... and 4 more

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