Revise in-memory database handling for modern SQLite

[gwynne]

SQLiteKit has for a long time depended on the use of SQLite's shared cache with in-memory databases to support opening multiple connections to such databases. However, SQLite has also for a long time specifically recommended the total omission of the shared cache, a recommendation which SQLiteNIO now follows as of vapor/sqlite-nio#51. Therefore, SQLiteKit now uses uniquely-named temporary files to emulate the feature when in-memory databases are requested.

Additional changes in this release:

• To match Vapor and SQLiteNIO, Swift 5.7 is now required.
• Updated the README and the API documentation.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.00000% with 24 lines in your changes missing coverage. Please review.

Project coverage is 83.33%. Comparing base (25b05d7) to head (d098b5c).
Report is 12 commits behind head on main.

Files	Patch %	Lines
Sources/SQLiteKit/SQLiteDataEncoder.swift	40.74%	16 Missing ⚠️
Sources/SQLiteKit/SQLiteConnection+SQLKit.swift	50.00%	3 Missing ⚠️
Sources/SQLiteKit/SQLiteDataDecoder.swift	88.23%	2 Missing ⚠️
Sources/SQLiteKit/SQLiteDialect.swift	75.00%	2 Missing ⚠️
Sources/SQLiteKit/SQLiteConnectionSource.swift	95.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #105       +/-   ##
===========================================
+ Coverage   68.37%   83.33%   +14.95%     
===========================================
  Files           7        7               
  Lines         234      222       -12     
===========================================
+ Hits          160      185       +25     
+ Misses         74       37       -37     

Files	Coverage Δ
Sources/SQLiteKit/SQLiteRow+SQLRow.swift	100.00% <100.00%> (+58.33%)	⬆️
Sources/SQLiteKit/SQLiteConnectionSource.swift	97.22% <95.00%> (+5.91%)	⬆️
Sources/SQLiteKit/SQLiteDataDecoder.swift	90.90% <88.23%> (+39.79%)	⬆️
Sources/SQLiteKit/SQLiteDialect.swift	86.66% <75.00%> (ø)
Sources/SQLiteKit/SQLiteConnection+SQLKit.swift	85.71% <50.00%> (ø)
Sources/SQLiteKit/SQLiteDataEncoder.swift	58.00% <40.74%> (+7.20%)	⬆️

[github-advanced-security]

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[penny-for-vapor]

These changes are now available in 4.4.0