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>

tools/make_test_sras.py

@@ -42,12 +42,12 @@ def _preamble(ymult_v: float, yoff_adc: float, yzero_v: float) -> bytes:
 
 
 def build(n_angles: int, seed: int, samples_per_frame: int,
-          geometry: list[tuple[int, int]] | None = None) -> tuple[bytes, dict]:
+          geometry: list[tuple[int, int]] | None = None,
+          bps: int = 1) -> tuple[bytes, dict]:
     rng = np.random.default_rng(seed)
     src_geom = geometry or _GEOMETRY
     geom = [src_geom[a % len(src_geom)] for a in range(n_angles)]
     n_ch = 3
-    bps = 1
 
     angles_deg = np.linspace(0.0, 60.0, n_angles, dtype=np.float32)
     # Distinct calibration per channel so a swapped-channel bug is visible.
@@ -100,7 +100,9 @@ def build(n_angles: int, seed: int, samples_per_frame: int,
                 block[r, 1, f] = np.int8((a * 7 + r * 3 + f) % 100 - 50)
                 block[r, 2, f] = np.int8((a * 5 + r * 11 + f * 2) % 120 - 60)
         waveforms.append(block)
-        out += block.tobytes()
+        # bps=2 stores the same values big-endian int16, exercising the
+        # reader's >i2 memmap path.
+        out += (block.astype(">i2") if bps == 2 else block).tobytes()
 
     meta = {
         "n_angles": n_angles,
@@ -119,8 +121,9 @@ def build(n_angles: int, seed: int, samples_per_frame: int,
 
 def write(path: Path, n_angles: int = 3, seed: int = 0,
           samples_per_frame: int = 64,
-          geometry: list[tuple[int, int]] | None = None) -> dict:
-    payload, meta = build(n_angles, seed, samples_per_frame, geometry)
+          geometry: list[tuple[int, int]] | None = None,
+          bps: int = 1) -> dict:
+    payload, meta = build(n_angles, seed, samples_per_frame, geometry, bps=bps)
     path.write_bytes(payload)
     return meta