Add support for Common Table Expressions

[gwynne]

These changes are now available in 3.31.0

CTEs (WITH clauses) are now supported by SELECT, INSERT, UPDATE, DELETE, and UNION queries, including subqueries. Test and docs coverage is 100%.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (25d8170) to head (db4789b).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #179   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           98       100    +2     
  Lines         2565      2635   +70     
=========================================
+ Hits          2565      2635   +70     

Files	Coverage Δ
...it/Builders/Implementations/SQLDeleteBuilder.swift	100.00% <100.00%> (ø)
...it/Builders/Implementations/SQLInsertBuilder.swift	100.00% <100.00%> (ø)
...Kit/Builders/Implementations/SQLUnionBuilder.swift	100.00% <100.00%> (ø)
...it/Builders/Implementations/SQLUpdateBuilder.swift	100.00% <100.00%> (ø)
...s/Prototypes/SQLCommonTableExpressionBuilder.swift	100.00% <100.00%> (ø)
...Builders/Prototypes/SQLSubqueryClauseBuilder.swift	100.00% <100.00%> (ø)
...Expressions/Clauses/SQLCommonTableExpression.swift	100.00% <100.00%> (ø)
Sources/SQLKit/Expressions/Queries/SQLDelete.swift	100.00% <100.00%> (ø)
Sources/SQLKit/Expressions/Queries/SQLInsert.swift	100.00% <100.00%> (ø)
Sources/SQLKit/Expressions/Queries/SQLSelect.swift	100.00% <100.00%> (ø)
... and 2 more

[MahdiBM]

I personally would have liked to have at least 1 test case with a real world complex query.

[gwynne]

I personally would have liked to have at least 1 test case with a real world complex query.

There, happy? One of them even revealed a bug 😜