Add PSQLRow multi decode

[fabianfett]

Follow up to #221 and required to make #219 easier to review.

Motivation

We want to efficiently parse Postgres types back into Swift types. The best way to do this is by iterating the ByteBuffer exactly once and calling decode for every row.

Changes

• Add a bash script that does the code generation for PSQLRow decode methods for us.

Result

It becomes very cheap to decode a complete PSQLRow.

[codecov-commenter]

Codecov Report

Merging #222 (c453ac1) into main (4937286) will decrease coverage by 0.72%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #222      +/-   ##
==========================================
- Coverage   43.19%   42.46%   -0.73%     
==========================================
  Files         119      120       +1     
  Lines        8210     9252    +1042     
==========================================
+ Hits         3546     3929     +383     
- Misses       4664     5323     +659     

Flag	Coverage Δ
unittests	42.46% <0.00%> (-0.73%)	⬇️

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

Impacted Files	Coverage Δ
Sources/PostgresNIO/New/PSQLRow-multi-decode.swift	0.00% <0.00%> (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%)	⬆️
...ources/PostgresNIO/Data/PostgresData+Numeric.swift	70.44% <0.00%> (+3.64%)	⬆️
... and 19 more

[gwynne]

I'll let the bash script pass 😉