feat(other): add grocery store cart model

[nickzerjeski]

Description

Add a grocery cart model with item management and dynamic total calculation.

Fixes #14050

Changes

• Added other/grocery_store_cart.py containing GroceryStoreCart with:
  • add_item
  • remove_item
  • total_price
• Added doctest examples validating core usage.

Validation

• python3 -m doctest -v other/grocery_store_cart.py

[algorithms-keeper]

Closing this pull request as invalid

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