[ENH] Add downwards compatibility CI workflow for deep_equals (#532)

[sid200727]

Reference Issues/PRs

Fixes sktime#532.

What does this implement/fix? Explain your changes.

Adds a new GitHub Actions workflow (.github/workflows/test_compat.yml) that tests deep_equals against older dependency versions using uv's --exclude-newer flag:

• numpy 1.x + pandas 1.x (resolved as of 2023-04-02)
• numpy 1.x + pandas 2.x (resolved as of 2024-06-15)

Runs on push/PR to main, weekly on Mondays, and manually via workflow dispatch.

Does your contribution introduce a new dependency? If yes, which one?

No. uv is already used in the project.

What should a reviewer concentrate their feedback on?

• The chosen cutoff dates for each matrix entry
• Whether python-version: "3.11" is appropriate for both jobs

Any other comments?

Existing CI covers numpy 2 + pandas 3. This fills the gap for older combinations legacy users may still rely on.

PR checklist

For all contributions

• I've reviewed the project documentation on contributing
• I've added myself to the list of contributors
• PR title starts with [CI/CD]

For code contributions

• N/A — CI/CD only change, no new Python code added.

Summary by Sourcery

CI:

• Introduce a dedicated GitHub Actions workflow to run deep_equals tests against legacy NumPy/pandas dependency combinations on pushes, pull requests, a weekly schedule, and manual dispatch.

[sourcery-ai]

Reviewer's Guide

Adds a new GitHub Actions workflow that runs targeted deep_equals tests against older NumPy/Pandas dependency combinations using uv with --exclude-newer, triggered on main branch pushes/PRs, weekly schedule, and manual dispatch, with concurrency and matrix-based job configuration.

File-Level Changes

Change	Details	Files
Introduce a new downwards-compatibility CI workflow for deep_equals using uv and a dependency-date matrix.	Add a GitHub Actions workflow configured to run on pushes and pull requests to main, a weekly cron schedule, and manual workflow dispatch Configure workflow permissions to read-only and enable concurrency cancellation per-ref Define a matrix job that runs deep_equals tests against two dependency sets differentiated by uv --exclude-newer cutoff dates to approximate numpy 1.x + pandas 1.x and numpy 1.x + pandas 2.x on Python 3.11 Set up steps to check out the repository, install uv, install the specified Python version, install project test dependencies with uv pip and the matrix-specific exclude-newer date, print the resolved dependency versions, and run pytest only for skbase/utils/tests/test_deep_equals.py	.github/workflows/test_compat.yml

Assessment against linked issues

Issue	Objective	Addressed	Explanation
sktime#532	Add a CI workflow that performs downwards compatibility testing for the deep_equals utility only, using older versions of numpy and pandas via uv's time-based cutoff functionality.	✅
sktime#532	Configure the compatibility tests to cover environments representing: (a) pre-NumPy 2.0, and (b) at least one time point each corresponding to pandas 1.x and pandas 2.x, while existing CI continues to cover NumPy 2.x and pandas 3.x.	✅

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[sourcery-ai]

Hey - I've left some high level feedback:

• The uv python install ${{ matrix.python-version }} step doesn’t actually guarantee that Python 3.11 is the interpreter used for uv pip install --system and pytest (they will likely use the runner’s default Python); consider either using actions/setup-python for 3.11 or pinning/selecting the uv-managed interpreter explicitly before installing/running tests.
• Since all matrix entries currently use the same Python version, you could simplify the matrix by moving python-version: "3.11" to the job level and only varying name and exclude_newer in the matrix, unless you expect to add differing Python versions soon.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The `uv python install ${{ matrix.python-version }}` step doesn’t actually guarantee that Python 3.11 is the interpreter used for `uv pip install --system` and `pytest` (they will likely use the runner’s default Python); consider either using `actions/setup-python` for 3.11 or pinning/selecting the `uv`-managed interpreter explicitly before installing/running tests.
- Since all matrix entries currently use the same Python version, you could simplify the matrix by moving `python-version: "3.11"` to the job level and only varying `name` and `exclude_newer` in the matrix, unless you expect to add differing Python versions soon.

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