Seperate out Testing Suite into Unit and Regression Testing

[harryswift01]

Summary

This PR updates SIST's test suite and CI, splitting tests into fast unit tests and regression tests, adding a set of scheduled CI workflows, and reporting combined Python + C++ coverage through Coveralls.

Changes

Split the test suite into tests/unit and tests/regression:

• Moved test_energetics.py/test_ir_finder.py (pure Python, no build needed) into tests/unit
• Moved test_cli.py/test_regression.py/test_legacy_entrypoints.py (need the compiled qsidd binaries and the real CLI) into tests/regression, along with tests/data/tests/reference
• Split conftest.py accordingly, tests/unit needs no fixtures at all, so tests/regression/conftest.py now holds everything that builds/runs the CLI
• tests/unit now runs standalone in under a second, with zero build or subprocess activity

Add CodeEntropy's scheduled CI workflows and mirror its README badges:

• daily.yaml (unit tests across Python 3.12/3.13/3.14), weekly-docs.yaml (docs build), update-copyright-years-in-license-file.yaml, and renamed the existing conda-build regression job to weekly-regression.yaml
• Updated README.md badges to match

Impact

• No behavioural change to SIST itself, this is entirely test/CI structure
• Coverage is now tracked for both the Python package and the C++ core