fix: prevent division-by-zero and integer overflow in partition()

[hieuit095]

Summary

Fixes a crash bug in partition() (connectorx/src/partition.rs) where invalid inputs cause a panic via:

1. Division by zero when num == 0 in the calculation (max - min + 1) / num
2. Integer overflow when extreme min/max values cause overflow in (max - min + 1) or i * partition_size

Both issues can be triggered by a caller passing a malicious or erroneous partition_query with num == 0.

Changes

• Guard num == 0: Returns a proper error instead of panicking on division by zero
• Guard inverted range (max < min): Returns a single safe query rather than looping infinitely
• Use checked_add/sub/mul: Prevents i64 overflow in partition boundary calculations
• Use saturating_add: Safely handles edge cases where partition_size would be 0

Impact

• Crash prevention (HIGH): Users calling partition_sql() or read_sql() with partition_query.num = 0 would previously get an unhandled panic
• Integer overflow safety (MEDIUM): Extreme min/max values could cause silent wrong partition boundaries

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[wangxiaoying]

Won't this result in multiple partitions with overlapping ranges? This may cause the wrong result.

[wangxiaoying]

Thanks @hieuit095 for the PR!

I think the partition num check and max-min+1 overflow looks good. But the clamping logic may cause the same range handled by multiple partitions and result in the wrong result. We could just throw an error on those cases.