Support positional and keyed batch results

[simPod]

Summary

• Preserve positional list batch results.
• Accept keyed arrays and ArrayAccess batch results.
• Resolve missing keyed values to null.
• Keep mixed and object keys compatible through positional or ArrayAccess results.
• Document both supported result forms.

Motivation

Backends often return associative results keyed by identifier and can omit missing records. Supporting both keyed and positional forms avoids forcing every batch function to rebuild a full ordered list.