feat(server): add bulk registration methods for async completions

Add convenience methods to AsyncSpecification for registering multiple completions at once:

- completions(List) for bulk registration from collections
- completions(AsyncCompletionSpecification...) for inline varargs registration

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

mcp/src/main/java/io/modelcontextprotocol/server/McpServer.java

@@ -517,6 +517,36 @@ public AsyncSpecification prompts(McpServerFeatures.AsyncPromptSpecification...
 			return this;
 		}
 
+		/**
+		 * Registers multiple completions with their handlers using a List. This method is
+		 * useful when completions need to be added in bulk from a collection.
+		 * @param completions List of completion specifications. Must not be null.
+		 * @return This builder instance for method chaining
+		 * @throws IllegalArgumentException if completions is null
+		 */
+		public AsyncSpecification completions(List<McpServerFeatures.AsyncCompletionSpecification> completions) {
+			Assert.notNull(completions, "Completions list must not be null");
+			for (McpServerFeatures.AsyncCompletionSpecification completion : completions) {
+				this.completions.put(completion.referenceKey(), completion);
+			}
+			return this;
+		}
+
+		/**
+		 * Registers multiple completions with their handlers using varargs. This method
+		 * is useful when completions are defined inline and added directly.
+		 * @param completions Array of completion specifications. Must not be null.
+		 * @return This builder instance for method chaining
+		 * @throws IllegalArgumentException if completions is null
+		 */
+		public AsyncSpecification completions(McpServerFeatures.AsyncCompletionSpecification... completions) {
+			Assert.notNull(completions, "Completions list must not be null");
+			for (McpServerFeatures.AsyncCompletionSpecification completion : completions) {
+				this.completions.put(completion.referenceKey(), completion);
+			}
+			return this;
+		}
+
 		/**
 		 * Registers a consumer that will be notified when the list of roots changes. This
 		 * is useful for updating resource availability dynamically, such as when new