[ENH] Generate synthetic stallion data for testing.

[RihaanBH-1810]

This PR solves #1840 by replacing the get_stallion_data which downloads the dataset with a function which generates a similar dataset for testing.

Reference Issues/PRs

#1840

What does this implement/fix? Explain your changes.

Replace get_stallion_data usage in tests with get_stallion_dummy_data to avoid repeated network downloads and support offline CI.

What should a reviewer concentrate their feedback on?

Is this the right approach for generating synthetic data for tests ?

Did you add any tests for the change?

No

Any other comments?

PR checklist

• The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.
  To run hooks independent of commit, execute pre-commit run --all-files