[SQLite-kit] Wrap expression defaults in parentheses

[aayushbaluni]

What's Changed

Fixes #5634

When drizzle-kit push recreates a SQLite table (e.g. to add a named UNIQUE constraint), expression defaults like datetime('now') are emitted without the parentheses SQLite requires:

-- Before (broken):
`created_at` text DEFAULT datetime('now')  -- SQLITE_ERROR: near "(": syntax error

-- After (fixed):
`created_at` text DEFAULT (datetime('now'))  -- valid SQLite

Root Cause

SQLiteCreateTableConvertor and SQLiteAlterTableAddColumnConvertor in sqlgenerator.ts interpolate column.default directly into the SQL without wrapping expression defaults. SQLite's grammar requires non-literal defaults (function calls, expressions) to be enclosed in parentheses.

Fix

Added wrapSqliteExprDefault() — a small helper that detects whether a default value is a simple literal (string, number, NULL, CURRENT_TIMESTAMP, etc.) or an expression, and wraps expressions in parentheses. Applied to both SQLiteCreateTableConvertor.convert() and SQLiteAlterTableAddColumnConvertor.convert().

Literal defaults (strings, numbers, booleans, CURRENT_TIMESTAMP) pass through unchanged — no double-wrapping.

Tests Added

Three new test cases in sqlite-columns.test.ts:

1. Expression defaults wrapped in parentheses during CREATE TABLE
2. Expression defaults wrapped in parentheses during ALTER TABLE ADD COLUMN
3. Literal defaults NOT double-wrapped (regression guard)

All existing SQLite tests (columns, tables, generated, checks, libsql) continue to pass.

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