Use simple expressions for join equality condition is supported

Now we can join with condition `t1.c1 >= t2.c1 * 1000` but not `t1.c1 = t2.c1 * 1000`.

Look at the SQL join condition parsing and evaluation code, likely in the query planner or executor. The issue indicates support for inequality joins but not equality with expressions. Find where join conditions are validated and extended to allow simple expressions like multiplication on the right side. Test with a join query using `t1.c1 = t2.c1 * 1000` to verify the fix.

索引モデルが issue の本文から書いたものです。