fix: correct SQLite div_i formula for small dividends

[prql-bot]

Problem

The SQLite div_i implementation used ROUND(ABS(a / b) - 0.5) * SIGN(a) * SIGN(b) to emulate floor division. When |a| < |b|, SQLite's integer / truncates to 0, so ABS(0) - 0.5 = -0.5, and ROUND(-0.5) = -1 (SQLite rounds away from zero). This produced -1 instead of the correct 0.

Solution

Replaced the formula with CAST(ABS(a * 1.0 / b) AS INTEGER) * SIGN(a) * SIGN(b). The * 1.0 forces float division, and CAST(... AS INTEGER) truncates toward zero — exactly the semantics needed for integer division.

Testing

• Added a regression test (sqlite_div_i_small_dividend) that compiles 1 // 2 targeting SQLite
• Verified the test fails with the old formula and passes with the fix
• All 633 prqlc tests pass, all book documentation tests pass

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Closes #5735 — automated triage

[prql-bot]

Duplicate of #5736 (by @queelius) — both PRs apply the same fix to the same line. One should be closed.

The fix itself is correct: * 1.0 forces float division before truncation, avoiding the ROUND(-0.5) = -1 edge case in SQLite.