Add canonical test suite for VAL operator (WIP)

Co-authored-by: fermga <203334638+fermga@users.noreply.github.com>

Author: Copilot

pyproject.toml

@@ -239,6 +239,10 @@ markers = [
   "slow: marks tests as slow (deselect with '-m \"not slow\"')",
   "benchmarks: run with 'pytest benchmarks --benchmark-only' to execute the benchmark suite",
   "stress: high-load deterministic stress coverage (select with '-m \"stress\"')",
+  "val: Tests specific to VAL (Expansion) operator",
+  "canonical: Tests validating canonical TNFR invariants",
+  "nodal_equation: Tests validating fundamental nodal equation",
+  "fractality: Tests validating fractal preservation",
 ]
 
 [tool.mypy]