add type hints to data classes and fix get_ydata override conflict

- signature-only type hints for ADC_Result, MeasurementResult,
  Accumulation, and the Drawable base class (x: ndarray | list, y: list)
- get_ydata now takes channel: int = 0 across the hierarchy
  (Drawable, Accumulation, MeasurementResult, Error_Result), fixing
  the LSP violation flagged by pyrefly
- widen _XArray alias to ndarray | list: internal copy constructors
  pass self.x[:] which is that union
- add hinted files to pyrefly project-includes

pyrefly errors in the covered files drop from 102 to 74; the rest is
PyTables stub noise and pre-existing latent bugs left for separate fixes.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

pyproject.toml

@@ -58,6 +58,9 @@ version = {attr = "damaris.__version__"}
 project-includes = [
     "src/damaris/experiments/Experiment.py",
     "src/damaris/experiments/dac.py",
+    "src/damaris/data/ADC_Result.py",
+    "src/damaris/data/MeasurementResult.py",
+    "src/damaris/data/Accumulation.py",
 ]
 search-path = ["src"]
 python-version = "3.11"