[mcp-server] Add reply tool call (#1643)

## Summary
Adds a new mcp tool call, `codex-reply`, so we can continue existing
sessions. This is a first draft and does not yet support sessions from
previous processes.

## Testing
- [x] tested with mcp client

codex-rs/mcp-server/Cargo.toml

@@ -33,6 +33,7 @@ tokio = { version = "1", features = [
     "rt-multi-thread",
     "signal",
 ] }
+uuid = { version = "1", features = ["serde", "v4"] }
 
 [dev-dependencies]
 assert_cmd = "2"