fix: expand slice args in raw Where/Expr placeholders

[Solaris-star]

Summary

Where("id NOT IN ?", []int{1,2,3}) previously bound the slice as a single argument, producing invalid SQL:

WHERE id NOT IN ?
-- args: [[1 2 3]]

Eq/NotEq helpers already expand list values into (?,?,?).

Fix

Route raw string predicates through Expr expansion, and teach Expr.ToSql to expand array/slice arguments into parenthesized placeholders (matching Eq/NotEq).

Test plan

• go test .
• TestExprListArgExpansion
• TestWhereRawSQLListArgExpansion

Fixes #383