feat: update testing framework to Vitest and add comprehensive tests for ColorPoint and Poline classes

- Changed the test script in package.json to use Vitest.
- Added a new test file for ColorPoint and Poline with extensive test cases covering initialization, color manipulation, and position functions.
- Updated PolineOptions to make anchorColors and numPoints optional.
- Added skipLibCheck to tsconfig.json for improved build performance.

Author: meodai

README.md

@@ -429,8 +429,8 @@ type PositionFunction = (t: number, reverse?: boolean) => number;
 
 // Options for creating a Poline instance
 type PolineOptions = {
-  anchorColors: Vector3[];
-  numPoints: number;
+  anchorColors?: Vector3[];  // Optional: defaults to random pair
+  numPoints?: number;        // Optional: defaults to 4
   positionFunction?: PositionFunction;
   positionFunctionX?: PositionFunction;
   positionFunctionY?: PositionFunction;

dist/index.d.ts

@@ -67,8 +67,8 @@ export declare class ColorPoint {
     shiftHue(angle: number): void;
 }
 export type PolineOptions = {
-    anchorColors: Vector3[];
-    numPoints: number;
+    anchorColors?: Vector3[];
+    numPoints?: number;
     positionFunction?: (t: number, invert?: boolean) => number;
     positionFunctionX?: (t: number, invert?: boolean) => number;
     positionFunctionY?: (t: number, invert?: boolean) => number;