[Feature]: Create the SIST 1.0.0 regression suite

[harryswift01]

Feature Request

Problem / Motivation

Future development needs a reliable way to detect changes to the current scientific results.

Manual comparison is not enough for ongoing refactoring, packaging, and feature work.

Proposed Solution

Create a small regression suite using representative SIST calculations and validated reference outputs.

Proposed Work

• Select representative input datasets.
• Generate reference outputs from the agreed 1.0.0 baseline.
• Identify the scientific values that should be compared.
• Define and document numerical tolerances.
• Add command-line smoke tests.
• Add numerical regression tests.
• Run the suite automatically in CI.

Done When

• Reference data and outputs are available.
• Important scientific results are checked automatically.
• Numerical tolerances are documented.
• Test failures clearly identify changed values.
• The tests run for pull requests and the default branch.
• The full suite passes against the baseline.