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/protocol/src/mcp.rs

@@ -1,14 +1,14 @@
+//! Types used when representing Model Context Protocol (MCP) values inside the
+//! Codex protocol.
+//!
+//! We intentionally keep these types TS/JSON-schema friendly (via `ts-rs` and
+//! `schemars`) so they can be embedded in Codex's own protocol structures.
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde::Serialize;
 use ts_rs::TS;
 
-/// Types used when representing Model Context Protocol (MCP) values inside the
-/// Codex protocol.
-///
-/// We intentionally keep these types TS/JSON-schema friendly (via `ts-rs` and
-/// `schemars`) so they can be embedded in Codex's own protocol structures.
-
+/// ID of a request, which can be either a string or an integer.
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(untagged)]
 pub enum RequestId {
@@ -26,6 +26,7 @@ impl std::fmt::Display for RequestId {
     }
 }
 
+/// Definition for a tool the client can call.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct Tool {
@@ -51,6 +52,7 @@ pub struct Tool {
     pub meta: Option<serde_json::Value>,
 }
 
+/// A known resource that the server is capable of reading.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct Resource {
@@ -80,6 +82,7 @@ pub struct Resource {
     pub meta: Option<serde_json::Value>,
 }
 
+/// A template description for resources available on the server.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct ResourceTemplate {
@@ -99,6 +102,7 @@ pub struct ResourceTemplate {
     pub mime_type: Option<String>,
 }
 
+/// The server's response to a tool call.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct CallToolResult {