Merge PSQLConnection into PostgresConnection

[fabianfett]

Motivation

We want to evolve our current public API instead of just replacing it.

Changes

• Merge PSQLConnection into PostgresConnection

Result

A cleaner public API

[codecov-commenter]

Codecov Report

Merging #240 (398ea3b) into main (43742ef) will increase coverage by 3.61%.
The diff coverage is 22.90%.

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
+ Coverage   39.99%   43.60%   +3.61%     
==========================================
  Files         116      115       -1     
  Lines        9467     9485      +18     
==========================================
+ Hits         3786     4136     +350     
+ Misses       5681     5349     -332     

Flag	Coverage Δ
unittests	43.60% <22.90%> (+3.61%)	⬆️

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

Impacted Files	Coverage Δ
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	19.60% <ø> (+1.42%)	⬆️
Sources/PostgresNIO/New/PSQLEventsHandler.swift	0.00% <0.00%> (-26.09%)	⬇️
...es/PostgresNIO/Connection/PostgresConnection.swift	11.83% <20.00%> (+11.83%)	⬆️
...nection State Machine/ConnectionStateMachine.swift	54.66% <48.27%> (+8.22%)	⬆️
Sources/PostgresNIO/New/PSQLChannelHandler.swift	61.83% <100.00%> (+10.66%)	⬆️
...ces/PostgresNIO/New/PostgresRow-multi-decode.swift	4.44% <0.00%> (+0.19%)	⬆️
Sources/PostgresNIO/Data/PostgresRow.swift	50.00% <0.00%> (+1.02%)	⬆️
...s/PostgresNIO/New/Data/Array+PostgresCodable.swift	94.68% <0.00%> (+1.06%)	⬆️
... and 26 more

[gwynne]

Love it ❤️