Load mat files

[Parvathy-jani]

Summary

Fixed a bug in el_paso/utils.py: .mat files saved in MATLAB's newer v7.3 format (secretly HDF5) couldn't be read by scipy, updated load_mat_data to try mat73 first (handles v7.3) and fall back to scipy.io.loadmat for older files.

Checklist

• SPDX header present on new/changed files, with yourself as SPDX-FileContributor.
• ruff check . / ruff format . and ty check pass (or pre-commit ran clean).
• Tests added/updated as needed; pytest -m basic (and/or -m visual) passes locally.
• README.md / CONTRIBUTING.md updated if this changes install steps, usage, or the processing-script list.
• pre-commit executed without any failures

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New processing recipe / satellite mission

• Mission/instrument:
• Data product(s):
• Related issue:

Checklist

• Recipe lives under el_paso/recipes/<mission>/ and follows the structure of an existing recipe (input handling, metadata, output to PRBEM-style standard names).
• el_paso/recipes/<mission>/__init__.py updated if a new module was added.
• README.md "Available processing scripts" list updated to include this recipe.
• Type hints added on new/changed code.
• A test covers the new recipe.
• If the recipe needs new reference/system test data, it's been added to the Zenodo dataset (or flagged in this PR for a maintainer to do so).
• If the recipe needs credentials/secrets to download data (e.g. ESA_CLIENT_ID), that's called out below.

Notes for reviewers

Bug fix

• Bug: [Brief description of the bug]
• Root cause: [Explanation of what caused the bug]
• Related issue: [Link to the related issue]

Reproduction

Checklist

• Changelog/docs updated if the fix changes documented behavior.

Notes for reviewers

Feature / enhancement

• Feature:
• Related issue/discussion:

Design notes

Checklist

• Public API additions have type hints and docstrings (Google convention, per ruff.toml).
• examples/minimal_example.py (or another example) updated if this changes the primary usage pattern.
• README.md updated if this changes install steps, usage, or the feature set described there.
• Backwards compatibility considered: existing recipes and tests still pass unmodified, or breaking changes are called out.

Notes for reviewers

Documentation

Checklist

• Content is accurate against current code behavior (commands, flags, file paths verified to still exist).
• Links checked (internal anchors and external URLs resolve).
• Code samples in docs actually run against the current API.
• No unrelated formatting churn mixed into the diff.

Notes for reviewers

Dependency bump / chore

• What changed:
• Why (security fix, new feature needed elsewhere, upstream deprecation, etc.):

Checklist

• pyproject.toml version constraint updated consistently.

• IRBEM build still succeeds if the change touches build hooks or Fortran toolchain.

• CI workflows (.github/workflows/*.yml) still pass; any workflow file changes tested via workflow_dispatch or a draft PR run.

• Changelog/release notes updated if this affects the published package.

Notes for reviewers

Miscellaneous