Fix: missing child info in batches

[ahuininga-orisha]

Fixes #126

Description

Fixed an issue where grouped export information was missing or incorrect when a batch boundary split a parent product from its children.

Testing Steps

Run an export for every combination of the following settings:

• Batch size and children batch size: 1 and 5000
• Grouped export: Enabled and Disabled

Expected Results

General Validation (Grouped & Non-Grouped)

• Product count in Tweakwise is identical regardless of batch size (1 vs 5000).
• Product information remains the same across all product types: Simple, Configurable, Bundle, and Grouped regardless of batch size (1 vs 5000).

Grouped Export

• Verify the groupcode is correct for all product types.
• Verify children of configurable products contain:
  • parent_url
  • parent_name
  • parent_visibility: Must include both the simple product's visibility (usually 1) and the parent's visibility (usually 4).

Non-Grouped Export

• Verify that Configurable, Bundle, and Grouped products contain data for all associated children (e.g., all available sizes are present).