Implement Basic `SimpleQuery` Handling

[MahdiBM]

Resolves #499

Checklist

• [x] Implement basic SimpleQuery handling.
• [x] Tests.
• [x] Fix decoding rows from a SimpleQuery response with text format.

~~Decoding rows from a simple-query response seems to fail for now, although no-row queries do succeed. I think because as described in Postgres docs, the returned format of data for simple-query is text, and PostgresNIO doesn't properly support that.~~

EDIT: For SimpleQuery only, I removed the line that forced formats to be binary, and things are working now. I'm not sure how well PostgresNIO supports the text format, but it works for strings and ints.

Not Implemented In This PR

• [ ] Multiple statements in a single SimpleQuery.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 82.83019% with 91 lines in your changes missing coverage. Please review.

Project coverage is 63.05%. Comparing base (ecbc3eb) to head (942a3cb).

Files with missing lines	Patch %	Lines
...ection State Machine/SimpleQueryStateMachine.swift	80.27%	58 Missing :warning:
...nection State Machine/ConnectionStateMachine.swift	83.07%	33 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
+ Coverage   62.16%   63.05%   +0.88%     
==========================================
  Files         130      131       +1     
  Lines       10422    10919     +497     
==========================================
+ Hits         6479     6885     +406     
- Misses       3943     4034      +91     

Files with missing lines	Coverage Δ
...es/PostgresNIO/Connection/PostgresConnection.swift	41.04% <100.00%> (+2.60%)	:arrow_up:
Sources/PostgresNIO/New/PSQLTask.swift	81.39% <100.00%> (+3.61%)	:arrow_up:
...urces/PostgresNIO/New/PostgresChannelHandler.swift	84.70% <100.00%> (+0.19%)	:arrow_up:
...stgresNIO/New/PostgresFrontendMessageEncoder.swift	100.00% <100.00%> (ø)
...nection State Machine/ConnectionStateMachine.swift	66.69% <83.07%> (+2.42%)	:arrow_up:
...ection State Machine/SimpleQueryStateMachine.swift	80.27% <80.27%> (ø)

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[fabianfett]

I wonder if a better way is to build a dedicated SimpleQueryStateMachine? Wdyt?

[MahdiBM]

@fabianfett i moved the stuff to that, mid-PR. There is a SimpleQueryStateMachine file, though in GitHub UI you might need to chase it and push that "Load diff" button.

[MahdiBM]

FWIW we're already using this function on prod and it's been working as it should. Of course we're not querying rows with multiple queries because that's not implemented. The tests should also be pretty good 🙂.