fix(encoding): filter out NULLs in encodeContainingArrayInvertedIndexSpans (#173046)

[waterWang]

Fixes #173046

Problem: When encodeContainingArrayInvertedIndexSpans encounters an array with NULL elements (e.g., ARRAY[NULL::TIMETZ]), it previously returned an empty SpanExpression with no spans. This caused the optimizer to generate an inverted index scan with no constraint, which the execution engine rejected with:

internal error: expected inverted index scan to have a constraint

Root cause: The HasNulls() check in encodeContainingArrayInvertedIndexSpans was too aggressive: it returned an empty SpanExpression for ALL arrays with NULLs, even those that also contain non-NULL elements. The empty SpanExpression caused the optimizer to generate an unconstrained inverted scan.

Fix: When the array has NULLs, filter them out using excludeNulls=true when calling encodeArrayInvertedIndexTableKeys, and generate spans for the remaining non-NULL elements. If all elements are NULL, return nil to let the optimizer fall back to a full table scan (which correctly returns no rows since NULL comparisons in SQL are unknown).

Reproduction:

CREATE TABLE t (a TIMETZ[]);
CREATE INVERTED INDEX t_a_inverted ON t (a);
SELECT 1 FROM t WHERE a @> ARRAY[NULL::TIMETZ]::TIMETZ[];

This previously errored with "expected inverted index scan to have a constraint". After the fix, it returns an empty result set without error.

The <@ (contained by) variant already worked correctly by using excludeNulls=true.

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[ZhouXing19]

Thanks for working on this!
We're already working on the fix internally, so closing this PR.