Download gra

[RoxGamba]

Add to the Waveform_GRA class a function to automatically download simulations from scholarsphere. Additionally, fix some naming issues that were inconsistent with other classes.

Breaks retrocompatibility: we get rid of the mtdt_path option and require a certain structure of the data to be able to load it.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[Copilot]

Pull request overview

Adds first-class support for downloading and loading GRAthena++ simulations from ScholarSphere via Waveform_GRA, and updates the expected on-disk data layout (breaking change) to align with other catalog loaders.

Changes:

• Added Waveform_GRA.download_simulation() plus supporting HTTP/HTML-scraping helpers to fetch and unpack GRA datasets.
• Updated Waveform_GRA initialization/metadata/hlm loading to assume a structured layout (GRA_BHBH_{ID}/{res}/...) and renamed rescale to nu_rescale.
• Added a new GRA download test and updated CI to install additional download dependencies.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 12 comments.

File	Description
PyART/catalogs/gra.py	Implements ScholarSphere download + adjusts metadata/hlm loading to the new directory structure.
tests/test_gra.py	Adds an integration-style test validating download + basic waveform structure.
.github/workflows/tests.yml	Updates CI dependencies to support the new download/test path.

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