[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/Cargo.lock

@@ -807,6 +807,7 @@ dependencies = [
  "toml 0.9.1",
  "tracing",
  "tracing-subscriber",
+ "uuid",
  "wiremock",
 ]