Dimensional constraints: dynamic dimension persistence, lock mark, display variables, DIMCONSTRAINT

The dynamic dimension of a dimensional constraint is now linked in the
drawing file (AcDbAssocDependency + AcDbAssocDimDependencyBody on the
constraint node), reread on load, hidden by DCHIDE/DYNCONSTRAINTDISPLAY
and never plotted; it carries a lock mark before its text. New
CONSTRAINTNAMEFORMAT and DYNCONSTRAINTDISPLAY variables and the
DIMCONSTRAINT option front end. A transformed entity whose own end points
a driving dimension measures keeps only the first constraint point, so a
scaled line returns to its dimension value.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/scene/mod.rs

@@ -2298,6 +2298,10 @@ pub struct Scene {
     /// CONSTRAINTNAMEFORMAT: what a dynamic dimension's text shows —
     /// 0 the parameter name, 1 the value, 2 `name=value`.
     pub constraint_name_format: u8,
+    /// DYNCONSTRAINTDISPLAY: whether dynamic dimensions draw at all.
+    pub dynamic_constraint_display: bool,
+    /// Dynamic dimensions DCHIDE or DYNCONSTRAINTDISPLAY 0 keep off screen.
+    hidden_dynamic_dimensions: HashSet<Handle>,
     /// Session-only visibility overrides for constraint glyphs.
     hidden_parametric_constraints: HashSet<(
         parametric_constraints::ParametricScope,
@@ -2629,6 +2633,8 @@ impl Scene {
             associative_hatch_source_cache: RefCell::new(None),
             parametric_constraints: Vec::new(),
             constraint_name_format: 2,
+            dynamic_constraint_display: true,
+            hidden_dynamic_dimensions: HashSet::default(),
             hidden_parametric_constraints: HashSet::default(),
             shown_parametric_constraints: HashSet::default(),
             named_parameters: named_parameters::ParameterTable::new(),
@@ -5538,6 +5544,7 @@ impl Scene {
         self.object_isolation.hides(handle)
             || self.preview_hidden.contains(&handle)
             || self.command_preview_hidden.contains(&handle)
+            || self.hidden_dynamic_dimensions.contains(&handle)
     }
 
     /// Replace the command-owned source hide set and refresh only handles whose