Add async option to PSQLRowStream

[fabianfett]

Motivation

To allow async/await querying we need to support AsyncSequences.

Changes

• Adds PSQLRowSequence
• Adjusts PSQLRowStream to support PSQLRowSequence

Result

• Internal async/await support added.

[codecov-commenter]

Codecov Report

Merging #206 (135c5bd) into main (e61d43c) will increase coverage by 7.12%.
The diff coverage is 89.38%.

@@            Coverage Diff             @@
##             main     #206      +/-   ##
==========================================
+ Coverage   39.99%   47.12%   +7.12%     
==========================================
  Files         118      119       +1     
  Lines        7693     8238     +545     
==========================================
+ Hits         3077     3882     +805     
+ Misses       4616     4356     -260     

Flag	Coverage Δ
unittests	47.12% <89.38%> (+7.12%)	⬆️

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

Impacted Files	Coverage Δ
Sources/PostgresNIO/New/PSQLRowStream.swift	84.54% <87.64%> (+13.71%)	⬆️
Sources/PostgresNIO/New/PSQLRowSequence.swift	89.73% <89.73%> (ø)
...urces/PostgresNIO/New/Data/Array+PSQLCodable.swift	94.68% <0.00%> (+1.06%)	⬆️
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	19.60% <0.00%> (+1.42%)	⬆️
Sources/PostgresNIO/New/PSQLConnection.swift	31.68% <0.00%> (+1.98%)	⬆️
...s/PostgresNIO/Message/PostgresMessageDecoder.swift	95.45% <0.00%> (+2.27%)	⬆️
...es/PostgresNIO/New/PSQLBackendMessageDecoder.swift	93.28% <0.00%> (+2.98%)	⬆️
...urces/PostgresNIO/New/Messages/ErrorResponse.swift	32.30% <0.00%> (+3.07%)	⬆️
...urces/PostgresNIO/New/Data/Float+PSQLCodable.swift	76.66% <0.00%> (+3.33%)	⬆️
Sources/PostgresNIO/New/PSQLBackendMessage.swift	96.63% <0.00%> (+3.36%)	⬆️
... and 18 more

[gwynne]

Aside from some minor nits, what amount of the state machine my brain can keep in its working set at one time seems fine, I have no issue with it.

[gwynne]

I suppose I'll have to live with it like this 🤣