DefaultMcpTransportSession#closeGracefully leaks resources on incomplete DELETE response

Bug description
When the MCP server is abnormal, the statement this.onClose.apply(this.sessionId.get()) in the closeGracefully method of DefaultMcpTransportSession.java throws an exception, so this.openConnections::dispose is never executed and may leak resources.

Environment
Java version: 21
mcp-bom: 0.11.3

Steps to reproduce
1、Create an McpSyncClient.
2、Execute client.initialize(); client.listTools();
3、Suspend the debugger at client.closeGracefully();
4、Make the MCP server unavailable.
5、Resume execution of client.closeGracefully();

Expected behavior
this.openConnections::dispose should always be executed.

Minimal Complete Reproducible example
McpSyncClient client = McpClient.sync(transport)
.requestTimeout(Duration.ofSeconds(10))
.build();

// Initialize connection
client.initialize();

// List available tools
ListToolsResult tools = client.listTools();

// Close client
client.closeGracefully();