[Bug] Nullability validation incorrectly checks children masked by null parents

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/paimon-cpp/issues) and found nothing similar.

### Paimon-cpp version

master

### Minimal reproduce step

`ArrowUtils::CheckNullabilityMatch` recursively checks complete Arrow child arrays.

For nested Arrow types, a null parent may still have physical child values. These
children are logically hidden and should not participate in nullability validation.
However, if a hidden child is null and its field is non-nullable, the current
implementation rejects the batch.

This affects nested STRUCT, LIST, MAP, and VECTOR fields and is inconsistent with
Java's logical row semantics.

### What doesn't meet your expectations?

Expected behavior:

- Ignore child values masked by a null parent.
- Reject null children when the parent is valid and the child is logically visible.

### Anything else?

_No response_

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

まず、ArrowUtils::CheckNullabilityMatch と、ネストされた STRUCT、LIST、MAP、VECTOR 配列を対象とするテストを見つけます。null の親が物理的に null の子を含むケースと、有効な親が null の子を公開するケースを確認します。マスクされた子は無視され、可視の non-nullable な子は拒否されれば完了です。

索引モデルが issue の本文から書いたものです。