feat: add prompts support to mcp-client, ahere to MCP spec for prompts

- add new endpoints `list_prompts` and `get_prompt` in the MCP client
- update prompt model in mcp-core to make `description` and `arguments`
  optional, following MCP spec

crates/mcp-client/src/client.rs

@@ -1,7 +1,7 @@
 use mcp_core::protocol::{
-    CallToolResult, Implementation, InitializeResult, JsonRpcError, JsonRpcMessage,
-    JsonRpcNotification, JsonRpcRequest, JsonRpcResponse, ListResourcesResult, ListToolsResult,
-    ReadResourceResult, ServerCapabilities, METHOD_NOT_FOUND,
+    CallToolResult, GetPromptResult, Implementation, InitializeResult, JsonRpcError,
+    JsonRpcMessage, JsonRpcNotification, JsonRpcRequest, JsonRpcResponse, ListPromptsResult,
+    ListResourcesResult, ListToolsResult, ReadResourceResult, ServerCapabilities, METHOD_NOT_FOUND,
 };
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -93,6 +93,10 @@ pub trait McpClientTrait: Send + Sync {
     async fn list_tools(&self, next_cursor: Option<String>) -> Result<ListToolsResult, Error>;
 
     async fn call_tool(&self, name: &str, arguments: Value) -> Result<CallToolResult, Error>;
+
+    async fn list_prompts(&self, next_cursor: Option<String>) -> Result<ListPromptsResult, Error>;
+
+    async fn get_prompt(&self, name: &str, arguments: Value) -> Result<GetPromptResult, Error>;
 }
 
 /// The MCP client is the interface for MCP operations.
@@ -346,4 +350,42 @@ where
         // https://modelcontextprotocol.io/docs/concepts/tools#error-handling-2
         self.send_request("tools/call", params).await
     }
+
+    async fn list_prompts(&self, next_cursor: Option<String>) -> Result<ListPromptsResult, Error> {
+        if !self.completed_initialization() {
+            return Err(Error::NotInitialized);
+        }
+
+        // If prompts is not supported, return an error
+        if self.server_capabilities.as_ref().unwrap().prompts.is_none() {
+            return Err(Error::RpcError {
+                code: METHOD_NOT_FOUND,
+                message: "Server does not support 'prompts' capability".to_string(),
+            });
+        }
+
+        let payload = next_cursor
+            .map(|cursor| serde_json::json!({"cursor": cursor}))
+            .unwrap_or_else(|| serde_json::json!({}));
+
+        self.send_request("prompts/list", payload).await
+    }
+
+    async fn get_prompt(&self, name: &str, arguments: Value) -> Result<GetPromptResult, Error> {
+        if !self.completed_initialization() {
+            return Err(Error::NotInitialized);
+        }
+
+        // If prompts is not supported, return an error
+        if self.server_capabilities.as_ref().unwrap().prompts.is_none() {
+            return Err(Error::RpcError {
+                code: METHOD_NOT_FOUND,
+                message: "Server does not support 'prompts' capability".to_string(),
+            });
+        }
+
+        let params = serde_json::json!({ "name": name, "arguments": arguments });
+
+        self.send_request("prompts/get", params).await
+    }
 }