Explicit dynamics core: central differences, one-point hex8 with hourglass control, nodal-pressure tet4, solve.explicit (M10 X1) (#27)

* Model: explicit dynamic steps (end time, increment scale and cap, output intervals, initial velocities, rigid walls, hourglass and bulk viscosity controls); deck writers refuse them

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

* fem: uniform-strain hex8 and tet4 kinematics, Flanagan–Belytschko hourglass shape vectors, element frequency bound

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

* Explicit solver crate (L2): central differences with lumped mass, one-point hex8 with Flanagan–Belytschko hourglass control, Bonet–Burton tet4, bulk viscosity, rigid walls, energy account; wave and impact verification

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

* Engine: solve.explicit and solve.history commands, explicit results in the session and solve.probe; cantilever period against the modal solver

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

* Docs: explicit solver in the architecture, roadmap (M10 started), parity and literature (Part H)

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

* Simplify: Model::select_step shared by both solvers, Procedure::sets/is_dynamic, fused per-increment passes without allocation, shared element tail, generic command caps

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

* Catalogue: solve.explicit is ready; solve.history beside solve.probe

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

* Rebase onto the implicit couplings work: Procedure is no longer Copy

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

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Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/fem/src/lib.rs

@@ -9,6 +9,8 @@
 //! - [`element`]: the element table, stiffness (full, reduced, incompatible modes), consistent
 //!   and lumped mass, body forces, integration-point stresses and their extrapolation to nodes;
 //! - [`face`]: consistent nodal forces of pressure on element faces;
+//! - [`uniform`]: uniform-strain (one-point) hexahedron and tetrahedron kinematics, hourglass
+//!   shape vectors and element frequency bounds for explicit dynamics;
 //! - [`dense`]: the small dense linear algebra inside an element.
 //!
 //! Conventions: three translational degrees of freedom per node, ordered node by node; stress
@@ -24,6 +26,7 @@ pub mod face;
 pub mod material;
 pub mod quadrature;
 pub mod shape;
+pub mod uniform;
 
 pub use element::{ELEMENT_TYPES, ElementType, Family, Formulation, PointStress, Solid, element_type};
 pub use material::{Elasticity, elasticity, von_mises};