Test and document saving movement datasets to Zarr

[Tushar7012]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
Closes #45. Movement datasets can be large and users working with cloud storage or chunked workflows need a way to persist datasets to disk beyond netCDF. Zarr is natively supported by xarray and is well-suited for these use cases. This PR tests and documents that support.

What does this PR do?

• Adds tests/test_integration/test_zarr.py with integration tests that verify movement datasets of various types (poses, bboxes, processed, derived variables, datetime index) can be saved to Zarr stores using xarray's native to_zarr() method and loaded back with open_zarr(), with full state preserved.
• Adds a Saving and loading with Zarr section to the Input/Output user guide, directing users to xarray's native methods and linking to the xarray Zarr docs.

No wrapper functions are introduced. This follows the same approach taken for netCDF in #606. No pyproject.toml changes are needed — zarr is already available via the xarray[io] extra, which is part of movement's core dependencies.

References

Closes #45
See also: #606 (the netCDF equivalent that this PR mirrors)

How has this PR been tested?

The Zarr round-trip has been tested in tests/test_integration/test_zarr.py, mirroring the structure of test_netcdf.py. The test suite covers:

• 8 dataset variants (poses, bboxes, processed, derived variables, datetime index) via test_ds_save_and_load_zarr
• A single DataArray round-trip via test_da_save_and_load_zarr
• 9 test cases total, all passing locally

The full test suite (1036 tests) passes with no regressions.

Is this a breaking change?

No.

Does this PR require an update to the documentation?

Yes — a Saving and loading with Zarr section has been added to docs/source/user_guide/input_output.md, immediately after the netCDF section.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8d49d6a) to head (ad16b30).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           38        38           
  Lines         2284      2284           
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  Hits          2284      2284           

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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