Feat/sub hourly mixed steps

[mathleur]

Description

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[Copilot]

Pull request overview

This PR appears to target support for “mixed” step coordinate values (e.g., sub-hourly steps alongside step-range strings) while also removing the previously experimental “dynamic grid / switching grids” functionality and related optional dependency wiring.

Changes:

• Updated sub-hourly step type-change logic and axis index-range selection to better tolerate mixed index types.
• Removed dynamic grid replacement code and deleted the switching-grid helper module.
• Tightened engine selection by erroring when an axis has no configured slicer; simplified some project tooling config.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pyproject.toml	Removes cffi from test extras and drops the switching_grids optional-dependency group.
polytope_feature/polytope.py	Raises a clearer error when an axis is missing an engine mapping.
polytope_feature/options.py	Removes dynamic_grid option and the runtime grid-replacement logic.
polytope_feature/datacube/transformations/datacube_type_change/datacube_type_change.py	Adjusts sub-hourly step parsing/sorting and de-duplicates output formatting.
polytope_feature/datacube/switching_grid_helper.py	Deletes the switching-grid helper implementation.
polytope_feature/datacube/datacube_axis.py	Reworks find_standard_indices_between to handle mixed-type index lists.
.pre-commit-config.yaml	Removes pinned default Python version entry and normalizes hook indentation.

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