fix(schema): prevent crash validating unions of object arrays

[xianjianlf2]

Problem

When a union of array types with object element bases (e.g. { objB: string }[] | { objC: string }[]) was validated against an array containing a non-object element, a TypeError: Cannot use 'in' operator was thrown.

Inside a union branch, traversal runs in fail-fast mode and ctx.currentErrorCount saturates at 1, so an intersection's basis (object/proto) failure guard (currentErrorCount > errorCount) could not detect a newly added error once an earlier element in the same branch had already errored. The sequence node then continued iterating and applied the element's structure check (key in data) to a primitive, throwing.

Fix

SequenceNode now mirrors StructureNode by bailing out of remaining elements in fail-fast mode, both in traverseApply and in its compiled output, so a failed element basis short-circuits before the unguarded in check runs. Top-level (non-fail-fast) validation is unchanged and still collects every element error.

Testing

Added a regression test in ark/type/__tests__/union.test.ts covering a union of object arrays validated against an array containing a non-object element, confirming it no longer throws and reports a proper validation error.

Closes #1458

[pullfrog]

✅ No new issues found.

Reviewed changes — this PR prevents a hard TypeError crash when validating a union of object arrays against an array containing a primitive element, by making SequenceNode bail out of further element traversal in fail-fast mode (e.g. inside a union branch), matching the behavior already implemented in StructureNode.

• SequenceNode.traverseApply now checks ctx.failFast && ctx.currentErrorCount > errorCount after each element and returns early, stopping traversal of later elements once one element has failed inside a fail-fast context.
• SequenceNode.compile now initializes an errorCount snapshot and emits js.returnIfFailFast() after each prefix, defaultable/optional, variadic, and postfix element in the generated Apply traversal, producing the compiled equivalent of the runtime short-circuit.
• Regression test added to ark/type/__tests__/union.test.ts covering both element-orderings from issue #1458.

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