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

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

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

@@ -105,7 +105,20 @@ impl<ManipulatorGroupId: crate::Identifier> Subpath<ManipulatorGroupId> {
 
 	/// Returns an iterator of the [Bezier]s along the `Subpath`.
 	pub fn iter(&self) -> SubpathIter<ManipulatorGroupId> {
-		SubpathIter { subpath: self, index: 0 }
+		SubpathIter {
+			subpath: self,
+			index: 0,
+			is_always_closed: false,
+		}
+	}
+
+	/// Returns an iterator of the [Bezier]s along the `Subpath` always considering it as a closed subpath.
+	pub fn iter_closed(&self) -> SubpathIter<ManipulatorGroupId> {
+		SubpathIter {
+			subpath: self,
+			index: 0,
+			is_always_closed: true,
+		}
 	}
 
 	/// Returns a slice of the [ManipulatorGroup]s in the `Subpath`.