Convert test scripts to pytest; extend the equivalence harness

- pyproject.toml replaces sras_viewer_requirements.txt (same pins) and
  adds a dev extra with pytest.
- tools/test_refactor.py, test_alignment.py, test_gui.py become
  tests/test_compute.py, tests/test_alignment.py, tests/test_gui.py with
  assertions preserved verbatim. test_gui.py stays one ordered
  integration sequence over a shared module-scoped window.
- check_equivalence.py: drop the dead pre-refactor monolith shim (and the
  _compute_angle_alignment alias it consumed), extend the pad sweep to
  (1, 2, 4, 8, 40), add legacy-v4 and big-endian int16 legs (new bps=2
  option in make_test_sras) so the padded FFT path and the >i2 memmap
  path are in the baseline before the FFT rewrite.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,35 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "sras-viewer"
+version = "0.1.0"
+description = "Viewer and processing tools for SRAS .sras scan files"
+requires-python = ">=3.12"
+dependencies = [
+    "PyQt6==6.10.2",
+    "numpy==2.4.1",
+    "matplotlib==3.10.8",
+    "scipy==1.18.0",
+    # Angle alignment only: masked FFT phase correlation (skimage.registration).
+    "scikit-image==0.26.0",
+    # Faster rfft backend; the viewer falls back to scipy.fft without it.
+    "pyFFTW==0.15.1",
+]
+
+[project.optional-dependencies]
+dev = ["pytest"]
+
+[tool.setuptools]
+py-modules = [
+    "sras_format",
+    "sras_compute",
+    "sras_workers",
+    "sras_viewer",
+    "sras_average",
+    "sras_edit_scans",
+]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]