add Galileo recipe

[sahiljhawar]

Summary

GSSC Galileo EMU recipe (solves #118 )

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.

Recipes needs GSSC_USER and GSSC_PASS

[DoctorRabbit55]

Hi Sahil. I think the test is not working as expected. Also, you probably want either electrons or protons, not both. So an argument is probably the best choice to switch between the two. Let's also look at some plots together before merging.

[sahiljhawar]

continued in #133