feat: replace custom mcp-types crate with equivalents from rmcp (#10349)

We started working with MCP in Codex before
https://crates.io/crates/rmcp was mature, so we had our own crate for
MCP types that was generated from the MCP schema:


8b95d3e082/codex-rs/mcp-types/README.md

Now that `rmcp` is more mature, it makes more sense to use their MCP
types in Rust, as they handle details (like the `_meta` field) that our
custom version ignored. Though one advantage that our custom types had
is that our generated types implemented `JsonSchema` and `ts_rs::TS`,
whereas the types in `rmcp` do not. As such, part of the work of this PR
is leveraging the adapters between `rmcp` types and the serializable
types that are API for us (app server and MCP) introduced in #10356.

Note this PR results in a number of changes to
`codex-rs/app-server-protocol/schema`, which merit special attention
during review. We must ensure that these changes are still
backwards-compatible, which is possible because we have:

```diff
- export type CallToolResult = { content: Array<ContentBlock>, isError?: boolean, structuredContent?: JsonValue, };
+ export type CallToolResult = { content: Array<JsonValue>, structuredContent?: JsonValue, isError?: boolean, _meta?: JsonValue, };
```

so `ContentBlock` has been replaced with the more general `JsonValue`.
Note that `ContentBlock` was defined as:

```typescript
export type ContentBlock = TextContent | ImageContent | AudioContent | ResourceLink | EmbeddedResource;
```

so the deletion of those individual variants should not be a cause of
great concern.

Similarly, we have the following change in
`codex-rs/app-server-protocol/schema/typescript/Tool.ts`:

```
- export type Tool = { annotations?: ToolAnnotations, description?: string, inputSchema: ToolInputSchema, name: string, outputSchema?: ToolOutputSchema, title?: string, };
+ export type Tool = { name: string, title?: string, description?: string, inputSchema: JsonValue, outputSchema?: JsonValue, annotations?: JsonValue, icons?: Array<JsonValue>, _meta?: JsonValue, };
```

so:

- `annotations?: ToolAnnotations` ➡️ `JsonValue`
- `inputSchema: ToolInputSchema` ➡️ `JsonValue`
- `outputSchema?: ToolOutputSchema` ➡️ `JsonValue`

and two new fields: `icons?: Array<JsonValue>, _meta?: JsonValue`

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/10349).
* #10357
* __->__ #10349
* #10356

codex-rs/exec/tests/event_processor_with_json_output.rs

@@ -56,6 +56,7 @@ use codex_exec::exec_events::Usage;
 use codex_exec::exec_events::WebSearchItem;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ModeKind;
+use codex_protocol::mcp::CallToolResult;
 use codex_protocol::models::WebSearchAction;
 use codex_protocol::plan_tool::PlanItemArg;
 use codex_protocol::plan_tool::StepStatus;
@@ -63,10 +64,8 @@ use codex_protocol::plan_tool::UpdatePlanArgs;
 use codex_protocol::protocol::CodexErrorInfo;
 use codex_protocol::protocol::ExecCommandOutputDeltaEvent;
 use codex_protocol::protocol::ExecOutputStream;
-use mcp_types::CallToolResult;
-use mcp_types::ContentBlock;
-use mcp_types::TextContent;
 use pretty_assertions::assert_eq;
+use rmcp::model::Content;
 use serde_json::json;
 use std::path::PathBuf;
 use std::time::Duration;
@@ -385,6 +384,7 @@ fn mcp_tool_call_begin_and_end_emit_item_events() {
                 content: Vec::new(),
                 is_error: None,
                 structured_content: None,
+                meta: None,
             }),
         }),
     );
@@ -499,13 +499,10 @@ fn mcp_tool_call_defaults_arguments_and_preserves_structured_content() {
             invocation,
             duration: Duration::from_millis(10),
             result: Ok(CallToolResult {
-                content: vec![ContentBlock::TextContent(TextContent {
-                    annotations: None,
-                    text: "done".to_string(),
-                    r#type: "text".to_string(),
-                })],
+                content: vec![serde_json::to_value(Content::text("done")).unwrap()],
                 is_error: None,
                 structured_content: Some(json!({ "status": "ok" })),
+                meta: None,
             }),
         }),
     );
@@ -520,11 +517,7 @@ fn mcp_tool_call_defaults_arguments_and_preserves_structured_content() {
                     tool: "tool_z".to_string(),
                     arguments: serde_json::Value::Null,
                     result: Some(McpToolCallItemResult {
-                        content: vec![ContentBlock::TextContent(TextContent {
-                            annotations: None,
-                            text: "done".to_string(),
-                            r#type: "text".to_string(),
-                        })],
+                        content: vec![serde_json::to_value(Content::text("done")).unwrap()],
                         structured_content: Some(json!({ "status": "ok" })),
                     }),
                     error: None,