config: {
  ...defaultSpringConfig,
  ...config,
}

import { spring } from 'remotion';

const value = spring({
  frame: 10,
  fps: 30,
  config: {
    damping: 10,
    stiffness: undefined,
  },
});

### Expected behavior

### Expected behavior
`springCalculation` should fall back to `defaultSpringConfig` values using nullish coalescing (`config.stiffness ?? defaultSpringConfig.stiffness`), gracefully handling partial and optional configuration objects.

### Suggested Fix
```diff
--- a/packages/core/src/spring/spring-utils.ts
+++ b/packages/core/src/spring/spring-utils.ts
@@ -14,7 +14,7 @@ export type SpringConfig = {
 	overshootClamping: boolean;
 };
 
-const defaultSpringConfig: SpringConfig = {
+export const defaultSpringConfig: SpringConfig = {
 	damping: 10,
 	mass: 1,
 	stiffness: 100,
@@ -118,12 +118,18 @@ export function springCalculation({
 	const from = 0;
 	const to = 1;
+	const resolvedConfig: SpringConfig = {
+		damping: config.damping ?? defaultSpringConfig.damping,
+		mass: config.mass ?? defaultSpringConfig.mass,
+		stiffness: config.stiffness ?? defaultSpringConfig.stiffness,
+		overshootClamping:
+			config.overshootClamping ?? defaultSpringConfig.overshootClamping,
+	};
 	const cacheKey = [
 		frame,
 		fps,
-		config.damping,
-		config.mass,
-		config.overshootClamping,
-		config.stiffness,
+		resolvedConfig.damping,
+		resolvedConfig.mass,
+		resolvedConfig.overshootClamping,
+		resolvedConfig.stiffness,
 	].join('-');
 	if (calculationCache[cacheKey]) {
 		return calculationCache[cacheKey];
@@ -144,10 +150,7 @@ export function springCalculation({
 		animation = advance({
 			animation,
 			now: time,
-			config: {
-				...defaultSpringConfig,
-				...config,
-			},
+			config: resolvedConfig,
 		});
 	}
 
@@ -156,10 +159,7 @@ export function springCalculation({
 		animation = advance({
 			animation,
 			now: (frameClamped / fps) * 1000,
-			config: {
-				...defaultSpringConfig,
-				...config,
-			},
+			config: resolvedConfig,
 		});
 	}