Continue to make forward progress when cancelled

[fabianfett]

Motivation

With the async/await interface we introduced the option to ignore a rowStream (by dropping the AsyncSequence or AsyncIterator). In those cases we must fail the stream and drain the connection ASAP. Otherwise we will lock up the connection.

Changes

• Drain connection, if the row stream was cancelled

Result

Connection is reusable, even if previous queries were cancelled.

Note:

Needs more unit tests

[codecov-commenter]

Codecov Report

Merging #261 (3e900c8) into main (ab624e4) will increase coverage by 0.72%.
The diff coverage is 60.83%.

@@            Coverage Diff             @@
##             main     #261      +/-   ##
==========================================
+ Coverage   43.85%   44.57%   +0.72%     
==========================================
  Files         115      115              
  Lines        9513     9639     +126     
==========================================
+ Hits         4172     4297     +125     
- Misses       5341     5342       +1     

Flag	Coverage Δ
unittests	44.57% <60.83%> (+0.72%)	⬆️

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

Impacted Files	Coverage Δ
Sources/PostgresNIO/Postgres+PSQLCompat.swift	0.00% <0.00%> (ø)
...urces/PostgresNIO/New/PostgresChannelHandler.swift	61.14% <18.18%> (-0.45%)	⬇️
...nnection State Machine/RowStreamStateMachine.swift	66.85% <58.69%> (-2.92%)	⬇️
...tion State Machine/ExtendedQueryStateMachine.swift	68.57% <64.28%> (+3.30%)	⬆️
...nection State Machine/ConnectionStateMachine.swift	57.54% <90.90%> (+2.88%)	⬆️
Sources/PostgresNIO/New/PSQLError.swift	76.31% <100.00%> (+0.97%)	⬆️
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	22.72% <0.00%> (+3.11%)	⬆️

[gwynne]

Two utterly pointless grammar nits just to annoy you 🙂, plus one minor functional nit, marking as changes requested in case there was an actual logic error there.

[gwynne]

My bad on the misread, approved!