Fix WITH using a CSV source to close #1276

[harsh-thakkar7]

Fix WITH using a CSV source (#1276)

Problem

WITH ... SELECT * FROM CSV('<file>', {headers:true}) throws:

Error: Data source number 0 in undefined

The CSV source is loaded from file asynchronously (loadFile), but yy.WithSelect.prototype.execute called w.select.execute(databaseid, params) without a callback, so the temporary table's data was still undefined when the outer select joined/read it.

Fix

WithSelect.execute now executes each non-recursive CTE with a completion callback: the temporary table is populated once the subquery finishes, and the next CTE / outer select only runs afterwards. Synchronous CTE queries complete during the call, so the sync path is unchanged and existing WITH tests are unaffected (submitted tests + existing CTE tests pass).

Tests

Added test/test1276.js with 4 cases:

• A) plain SELECT * FROM CSV("./test/test1276.csv", ...) baseline
• B) WITH c AS (SELECT * FROM CSV(...)) SELECT * FROM c
• C) B returns exactly what A returns
• D) several CTEs over CSV sources

$ bun test --preload ./test/bun-setup.js ./test/test1276.js
 4 pass
 0 fail

Because the bug is triggered by the async path, the tests assert via alasql.promise (as the original repro used alasql with callbacks/then).

Closes #1276