generate an internal json schema for RolloutLine (#14434)

### Why
i'm working on something that parses and analyzes codex rollout logs,
and i'd like to have a schema for generating a parser/validator.

`codex app-server generate-internal-json-schema` writes an
`RolloutLine.json` file

while doing this, i noticed we have a writer <> reader mismatch issue on
`FunctionCallOutputPayload` and reasoning item ID -- added some schemars
annotations to fix those

### Test

```
$ just codex app-server generate-internal-json-schema --out ./foo
```

generates an `RolloutLine.json` file, which i validated against jsonl
files on disk

`just codex app-server --help` doesn't expose the
`generate-internal-json-schema` option by default, but you can do `just
codex app-server generate-internal-json-schema --help` if you know the
command

everything else still works

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-protocol/src/lib.rs

@@ -6,6 +6,7 @@ mod schema_fixtures;
 
 pub use experimental_api::*;
 pub use export::GenerateTsOptions;
+pub use export::generate_internal_json_schema;
 pub use export::generate_json;
 pub use export::generate_json_with_experimental;
 pub use export::generate_ts;