feat(query): add immutable SQL query builder module

[ConsoleTVs]

Summary

New query module providing an immutable, copy-on-write SQL query builder with zero dependencies.

Features

• SELECT with columns, joins, WHERE, GROUP BY, ORDER BY, LIMIT, OFFSET
• INSERT with column-value pairs
• UPDATE with SET and WHERE
• DELETE with WHERE
• Raw expressions via Raw (literal SQL) and Expr (SQL with placeholders)
• Immutable — each method returns a new value, safe to derive from shared bases
• ? placeholders — compatible with sqlx rebind for any database

Usage

sql, args := query.Select("users").
    Columns("id", "name", query.Raw("COUNT(*) AS total")).
    Join("posts ON posts.user_id = users.id").
    Where("active = ?", true).
    GroupBy("users.id").
    OrderBy("total DESC").
    Limit(10).
    Build()

db.Select(ctx, sql, &users, args...)

Coverage

100% statement coverage.