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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #179 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 98 100 +2 Lines 2565 2635 +70 ========================================= + Hits 2565 2635 +70 ``` | [Files](https://app.codecov.io/gh/vapor/sql-kit/pull/179?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [...it/Builders/Implementations/SQLDeleteBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FImplementations%2FSQLDeleteBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvSW1wbGVtZW50YXRpb25zL1NRTERlbGV0ZUJ1aWxkZXIuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [...it/Builders/Implementations/SQLInsertBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FImplementations%2FSQLInsertBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvSW1wbGVtZW50YXRpb25zL1NRTEluc2VydEJ1aWxkZXIuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [...Kit/Builders/Implementations/SQLUnionBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FImplementations%2FSQLUnionBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvSW1wbGVtZW50YXRpb25zL1NRTFVuaW9uQnVpbGRlci5zd2lmdA==) | `100.00% <100.00%> (ø)` | | | [...it/Builders/Implementations/SQLUpdateBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FImplementations%2FSQLUpdateBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvSW1wbGVtZW50YXRpb25zL1NRTFVwZGF0ZUJ1aWxkZXIuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [...s/Prototypes/SQLCommonTableExpressionBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FPrototypes%2FSQLCommonTableExpressionBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvUHJvdG90eXBlcy9TUUxDb21tb25UYWJsZUV4cHJlc3Npb25CdWlsZGVyLnN3aWZ0) | `100.00% <100.00%> (ø)` | | | [...Builders/Prototypes/SQLSubqueryClauseBuilder.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FBuilders%2FPrototypes%2FSQLSubqueryClauseBuilder.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvQnVpbGRlcnMvUHJvdG90eXBlcy9TUUxTdWJxdWVyeUNsYXVzZUJ1aWxkZXIuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [...Expressions/Clauses/SQLCommonTableExpression.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FExpressions%2FClauses%2FSQLCommonTableExpression.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvRXhwcmVzc2lvbnMvQ2xhdXNlcy9TUUxDb21tb25UYWJsZUV4cHJlc3Npb24uc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [Sources/SQLKit/Expressions/Queries/SQLDelete.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FExpressions%2FQueries%2FSQLDelete.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvRXhwcmVzc2lvbnMvUXVlcmllcy9TUUxEZWxldGUuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [Sources/SQLKit/Expressions/Queries/SQLInsert.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FExpressions%2FQueries%2FSQLInsert.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvRXhwcmVzc2lvbnMvUXVlcmllcy9TUUxJbnNlcnQuc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | [Sources/SQLKit/Expressions/Queries/SQLSelect.swift](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree&filepath=Sources%2FSQLKit%2FExpressions%2FQueries%2FSQLSelect.swift&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9TUUxLaXQvRXhwcmVzc2lvbnMvUXVlcmllcy9TUUxTZWxlY3Quc3dpZnQ=) | `100.00% <100.00%> (ø)` | | | ... and [2 more](https://app.codecov.io/gh/vapor/sql-kit/pull/179?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | |

[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 😜