Inherit parent context in coRouter DSL

This commit also allows context override, as it
is useful for the nested router use case.

Closes gh-31831

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/CoRouterFunctionDsl.kt

@@ -144,7 +144,7 @@ class CoRouterFunctionDsl internal constructor (private val init: (CoRouterFunct
 	 * @see RouterFunctions.nest
 	 */
 	fun RequestPredicate.nest(r: (CoRouterFunctionDsl.() -> Unit)) {
-		builder.add(nest(this, CoRouterFunctionDsl(r).build()))
+		builder.add(nest(this, CoRouterFunctionDsl(r).also { it.contextProvider = contextProvider }.build()))
 	}
 
 
@@ -628,9 +628,6 @@ class CoRouterFunctionDsl internal constructor (private val init: (CoRouterFunct
 	 * @since 6.1
 	 */
 	fun context(provider: suspend (ServerRequest) -> CoroutineContext) {
-		if (this.contextProvider != null) {
-			throw IllegalStateException("The Coroutine context provider should not be defined more than once")
-		}
 		this.contextProvider = provider
 	}