Refactor SQLiteConnection.swift to support readonly mode for file-bas…

[vi4m]

Readonly option for sqlite

[0xTim]

I think we can get away with this. @gwynne any thoughts?

[codecov]

Codecov Report

Attention: Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.

Project coverage is 66.20%. Comparing base (7353cca) to head (f467879).

Files with missing lines	Patch %	Lines
Sources/SQLiteNIO/SQLiteConnection.swift	61.53%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
- Coverage   66.28%   66.20%   -0.08%     
==========================================
  Files           9        9              
  Lines         777      787      +10     
==========================================
+ Hits          515      521       +6     
- Misses        262      266       +4     

Files with missing lines	Coverage Δ
Sources/SQLiteNIO/SQLiteConnection.swift	68.33% <61.53%> (-0.76%)	⬇️

[gwynne]

Could use a test

[gwynne]

Also the API breakage checker has a halfway-valid complaint, for once 🤨