Move tolerance to geometry

It is starting to see use there, and I think it makes more sense for
`approx` to depend on `geometry` than the other way around. `geometry`
can be seen to provide low-level geometry primitives, which `approx`,
which is higher-level functionality, should depend on at some point.

crates/fj-core/src/algorithms/approx/mod.rs

@@ -6,7 +6,6 @@ pub mod half_edge;
 pub mod shell;
 pub mod sketch;
 pub mod solid;
-pub mod tolerance;
 
 mod circle;
 mod curve;
@@ -25,10 +24,8 @@ use vertex::VertexApproxCache;
 
 use crate::geometry::Geometry;
 
-pub use self::{
-    circle::PathApproxParams,
-    tolerance::{InvalidTolerance, Tolerance},
-};
+pub use self::circle::PathApproxParams;
+pub use crate::geometry::{InvalidTolerance, Tolerance};
 
 /// Approximate an object
 pub trait Approx: Sized {

crates/fj-core/src/geometry/mod.rs

@@ -5,6 +5,7 @@ mod curve;
 mod geometry;
 mod path;
 mod surface;
+mod tolerance;
 mod vertex;
 
 pub use self::{
@@ -13,5 +14,6 @@ pub use self::{
     geometry::Geometry,
     path::Path,
     surface::SurfaceGeom,
+    tolerance::{InvalidTolerance, Tolerance},
     vertex::{LocalVertexGeom, VertexGeom},
 };