fix(blocks): add offset option to Pods Item List and Related Item List blocks

[faisalahammad]

Summary

Adds an Offset field to the Pods Item List and Related Item List blocks, allowing users to skip a number of items when listing the same pod in multiple places. The underlying [pods] shortcode and data layer already support offset, so this only exposes the existing parameter through the block UI.

Fixes #7523

Changes

Item List block

Before:
No offset field; users could only set a limit.

After:
Added offset field (type number, default 0) in src/Pods/Blocks/Types/Item_List.php and mapped it in the shortcode transform. Added offset attribute to ui/js/blocks/block-types/pods-block-list/block.json.

Why: Lets users skip N items before rendering the list without writing a custom shortcode.

Related Item List block

Before:
No offset field.

After:
Added offset field (type number, default 0) in src/Pods/Blocks/Types/Related_Item_List.php.

Why: Same list block family, uses the same shortcode path and limit field.

Testing

Test 1: Item List block with offset

1. Add Pods Item List block, choose pod/template, set Limit 2 and Offset 1.
2. View page.
   Result: shows items 2-3, skipping item 1.

Test 2: Related Item List block with offset

1. Add Pods Related Item List block, choose related field/template, set Limit 2 and Offset 1.
2. View page.
   Result: skips first related item and shows next 2.

Test 3: Shortcode transform

1. Insert [pods name="my_pod" limit="2" offset="3" template="my_template"].
2. Transform to Pods Item List block.
   Result: Offset field shows 3.

Also ran php -l on changed files, validated JSON, and ran npm run build-production successfully. JS lint npm run lint-js fails due to a pre-existing missing parent eslint config (wordpress), not from this change.