feat(other): add grocery store cart model (v2)

[nickzerjeski]

Describe your change:

Fixes #14050

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[algorithms-keeper]

Multiple Pull Request Detected

@nickzerjeski, we are extremely excited that you want to submit multiple algorithms in this repository but we have a limit on how many pull request a user can keep open at a time. This is to make sure all maintainers and users focus on a limited number of pull requests at a time to maintain the quality of the code.

This pull request is being closed as the user already has an open pull request. Please focus on your previous pull request before opening another one. Thank you for your cooperation.

User opened pull requests (including this one): #14547, #14546, #14545, #14537, #14536, #14535

[Copilot]

Pull request overview

Adds a small, reusable “grocery cart” model in other/ that encapsulates cart state (item quantities) and pricing logic, aligned with the “console-free” requirement from the linked issue.

Changes:

• Introduces GroceryStoreCart to track item quantities against a provided price catalog.
• Adds add/remove operations with basic validation and exception signaling.
• Adds doctest-based examples and a __main__ doctest runner.

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[Copilot]

The doctest examples only cover the happy path. CONTRIBUTING.md asks for doctests that cover erroneous input values too; please add doctests for cases like empty price_catalog, unknown item in add_item(), and non-positive quantities to ensure exception behavior is tested and stays stable.

Suggested change

	3.5
	3.5
	>>> GroceryStoreCart({})
	Traceback (most recent call last):
	...
	ValueError: price_catalog cannot be empty
	>>> cart = GroceryStoreCart({"apple": 1.5})
	>>> cart.add_item("banana")
	Traceback (most recent call last):
	...
	KeyError: "'banana' is not in the catalog"
	>>> cart.add_item("apple", 0)
	Traceback (most recent call last):
	...
	ValueError: quantity must be positive
	>>> cart.add_item("apple", -1)
	Traceback (most recent call last):
	...
	ValueError: quantity must be positive

[Copilot]

remove_item() silently removes the item when quantity exceeds the current quantity (because remaining <= 0 falls into the pop() branch). This can hide caller mistakes; consider raising ValueError when quantity > current (or explicitly documenting/clamping the behavior) and add a doctest for the chosen behavior.