fix: set struct parent validity when writing struct for lance v2.1+

[qidian99]

Fix #119

[github-actions]

ACTION NEEDED
Lance follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message. Please update your PR title and description to match the specification.

For details on the error please inspect the "PR Title Check" action.

[chatgpt-codex-connector]

💡 Codex Review

lance-spark/lance-spark-base_2.12/src/main/scala/com/lancedb/lance/spark/arrow/LanceArrowWriter.scala

Lines 391 to 394 in b1c4c9a

	override def setNull(): Unit = {
	// mark the parent struct as null for this row
	valueVector.setNull(count)
	}

Propagate struct null rows to children

When a struct column contains null rows, setNull only clears the parent validity bit and never advances the child writers, while setValue now marks later rows as defined. After a null struct row the parent’s count increments but the children’s counts stay behind, so subsequent non-null structs are reported as valid but their children reside at earlier indexes (or are absent), leading to misaligned data or IndexOutOfBounds when consumers read the record batch. setNull needs to also write nulls for each child to keep child value counts aligned with the parent for every row.

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".