Reject listRoots if not supported by client, without sending any request

[michaelboyles]

Some requests in McpAsyncServerExchange make a point of failing fast if functionality not supported, such the condition on line 146

java-sdk/mcp-core/src/main/java/io/modelcontextprotocol/server/McpAsyncServerExchange.java

Lines 141 to 151 in fd00498

	public Mono<McpSchema.CreateMessageResult> createMessage(McpSchema.CreateMessageRequest createMessageRequest) {
	if (this.clientCapabilities == null) {
	return Mono
	.error(new IllegalStateException("Client must be initialized. Call the initialize method first!"));
	}
	if (this.clientCapabilities.sampling() == null) {
	return Mono.error(new IllegalStateException("Client must be configured with sampling capabilities"));
	}
	return this.session.sendRequest(McpSchema.METHOD_SAMPLING_CREATE_MESSAGE, createMessageRequest,
	CREATE_MESSAGE_RESULT_TYPE_REF);
	}

listRoots does not do the same

java-sdk/mcp-core/src/main/java/io/modelcontextprotocol/server/McpAsyncServerExchange.java

Lines 227 to 230 in fd00498

	public Mono<McpSchema.ListRootsResult> listRoots(String cursor) {
	return this.session.sendRequest(McpSchema.METHOD_ROOTS_LIST, new McpSchema.PaginatedRequest(cursor),
	LIST_ROOTS_RESULT_TYPE_REF);
	}

For example, add this

if (this.clientCapabilities.roots() == null) { 
    return Mono.error(new IllegalStateException("Client must be configured with root listing capabilities")); 
}