Bezier-rs: Add calculations for area and centroid of subpaths (#1729)

* add code to calculate area and centroid of subpath

* change library to poly_it

* add a demo of area and centroid

* modify algorithm to consider negetive area as positive

* add code for manipulating polynomials in bezier-rs

* remove `poly_it` dependency and use custom Polynomial

* formatting floats to skip last zero

* add debug mechanism

* collect both intersection points instead of one

* fix test and cargo fmt

* apply minimum separation filtering in self_intersection and use better endpoint filtering algorithm

* remove debug mechanism and cargo fmt

* consider the subpath as closed for intersection calculation

* add documentation for polynomial.rs

* impl display for Polynomial

* make area always positive

* add missing docs

* fix test and cargo fmt

* Naming/formatting code review

---------

Co-authored-by: Keavon Chambers <keavon@keavon.com>

libraries/bezier-rs/src/subpath/mod.rs

@@ -29,6 +29,7 @@ unsafe impl<ManipulatorGroupId: crate::Identifier> dyn_any::StaticType for Subpa
 pub struct SubpathIter<'a, ManipulatorGroupId: crate::Identifier> {
 	index: usize,
 	subpath: &'a Subpath<ManipulatorGroupId>,
+	is_always_closed: bool,
 }
 
 impl<ManipulatorGroupId: crate::Identifier> Index<usize> for Subpath<ManipulatorGroupId> {
@@ -55,8 +56,9 @@ impl<ManipulatorGroupId: crate::Identifier> Iterator for SubpathIter<'_, Manipul
 		if self.subpath.is_empty() {
 			return None;
 		}
+		let closed = if self.is_always_closed { true } else { self.subpath.closed };
 		let len = self.subpath.len() - 1
-			+ match self.subpath.closed {
+			+ match closed {
 				true => 1,
 				false => 0,
 			};