Explicit X2: large deformation, J2 and Johnson-Cook plasticity, damage and erosion (M10)

- model: materials gain solver-neutral plastic (bilinear isotropic/kinematic,
  hardening table, Johnson-Cook with adiabatic heating), damage (Johnson-Cook
  D1-D5) and erosion (plastic strain); explicit steps gain nonlinear_geometry
  (default on) and stress_rate (jaumann | green_naghdi).
- fem: rotation (Hughes-Winget, Flanagan-Taylor), plasticity (radial return,
  capped bracketed Newton for Johnson-Cook, damage; the update takes the
  mechanical strain increment so thermal strains can be subtracted), closed-form
  hex8 gradients for deformed configurations.
- explicit: updated Lagrangian hex8/tet4, per-element material state, erosion
  with reported energy, plastic work in the energy account.
- solver: warns that the linear solver uses the elastic constants of plastic
  materials (results hash-identical).
- decks: Abaqus *PLASTIC (+ Johnson-Cook keywords), Nastran MATS1/TABLES1,
  LS-DYNA *MAT_PLASTIC_KINEMATIC / *MAT_PIECEWISE_LINEAR_PLASTICITY; what a
  format cannot express is reported as Unsupported.
- engine: model.material.plasticity, model.material.damage (catalogue ready),
  explicit element probe, eroded elements in the solve summary.

Step commits before the rebase onto the DOF framework: branch explicit-x2-steps.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/solver/src/system.rs

@@ -468,3 +468,17 @@ fn body(f: &mut [f64], mesh: &Mesh, e: &Elem, b: [f64; 3]) -> Result<()> {
     }
     Ok(())
 }
+
+/// The linear solver uses the elastic constants alone: a warning for each material in use whose
+/// plasticity, damage or erosion it leaves out.
+pub fn inelastic_warnings(model: &Model) -> Vec<String> {
+    let used: BTreeSet<&str> = model.sections().values().map(|s| s.material.as_str()).collect();
+    used.into_iter()
+        .filter(|name| model.material(name).is_some_and(|m| m.plastic.is_some() || m.damage.is_some() || m.erosion.is_some()))
+        .map(|name| {
+            format!(
+                "material `{name}`: the linear solver uses its elastic constants only (its plasticity, damage and erosion act in explicit dynamics)"
+            )
+        })
+        .collect()
+}