fix(dxf): resolve strict Clippy findings without weakening checks

Remove an unused private Interval helper and collapse the copied-vertex
guard to an equivalent let-chain with identical evaluation order and error.
Preserve all 28 geometry and 10 bounds tests, limits and assertions.

The prior a7f3c78b development attempt stopped at Clippy; IO/engine tests
and wasm were not reached. Both corrective hunks were source-reviewed,
and normal formatting passed. Tests for this new source remain unrun.

crates/io/src/dxf_out/file_model/bulges.rs

@@ -37,10 +37,6 @@ impl Interval {
         Self::checked(value, value)
     }
 
-    fn is(self, value: f64) -> bool {
-        self.lo == value && self.hi == value
-    }
-
     fn rounded(value: f64) -> Result<Self> {
         if value == 0.0 || !value.is_normal() {
             return Err(invalid("support arithmetic overflow or underflow"));

crates/io/src/dxf_out/file_model/geometry.rs

@@ -242,10 +242,11 @@ fn transformed_shape(shape: &DxfShape, scale: f64, translation: Vec2) -> Result<
             let mut previous: Option<(Vec2, Vec2)> = None;
             for vertex in vertices {
                 let at = transformed_point(vertex.at, scale, translation)?;
-                if let Some((old, last)) = previous {
-                    if old != vertex.at && last == at {
-                        return Err(invalid("DXF transform collapses adjacent distinct bulged vertices"));
-                    }
+                if let Some((old, last)) = previous
+                    && old != vertex.at
+                    && last == at
+                {
+                    return Err(invalid("DXF transform collapses adjacent distinct bulged vertices"));
                 }
                 copied.push(DxfVertex { at, bulge: vertex.bulge });
                 previous = Some((vertex.at, at));