Rename PostgresChannelHandler

[fabianfett]

Same old story: Drop PSQL prefix, use Postgres prefix.

[codecov-commenter]

Codecov Report

Merging #251 (e9912c1) into main (1cd8d36) will increase coverage by 4.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #251      +/-   ##
==========================================
+ Coverage   39.78%   43.82%   +4.03%     
==========================================
  Files         115      115              
  Lines        9513     9520       +7     
==========================================
+ Hits         3785     4172     +387     
+ Misses       5728     5348     -380     

Flag	Coverage Δ
unittests	43.82% <0.00%> (+4.03%)	⬆️

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

Impacted Files	Coverage Δ
...es/PostgresNIO/Connection/PostgresConnection.swift	17.48% <0.00%> (+0.93%)	⬆️
Sources/PostgresNIO/New/PSQLEventsHandler.swift	0.00% <ø> (ø)
...urces/PostgresNIO/New/PostgresChannelHandler.swift	61.83% <ø> (ø)
...ces/PostgresNIO/New/PostgresRow-multi-decode.swift	4.44% <0.00%> (+0.19%)	⬆️
Sources/PostgresNIO/Data/PostgresRow.swift	50.00% <0.00%> (+1.02%)	⬆️
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	19.60% <0.00%> (+1.42%)	⬆️
...s/PostgresNIO/New/Data/Array+PostgresCodable.swift	93.25% <0.00%> (+2.24%)	⬆️
...ostgresNIO/Deprecated/PostgresMessageDecoder.swift	95.45% <0.00%> (+2.27%)	⬆️
...ostgresNIO/New/PostgresBackendMessageDecoder.swift	93.28% <0.00%> (+2.98%)	⬆️
... and 23 more

[gwynne]

Barely know why approval should be required on this kind of thing 😁