[codex] Add RL trajectory capture

[Lixtt]

Summary

Adds opt-in RL trajectory capture to a3s-code so agent runs can emit structured JSONL records for downstream RL/SFT data construction.

Changes

• add RlTrajectoryRecorder and a3s.rl_trajectory.v1 JSONL event schema
• record execution lifecycle, LLM request/response, context compaction, tool calls, tool results, and parse/duplicate-call errors
• expose trajectory controls through Rust session options and Python SDK session options
• add focused tests for recorder behavior and Python SDK option mapping

Validation

• cargo fmt --check
• cargo test -p a3s-code-core rl_trajectory --lib
• LD_LIBRARY_PATH=/mnt/shared-storage-user/lixiangtian/miniconda3/lib:${LD_LIBRARY_PATH:-} cargo test --manifest-path sdk/python/Cargo.toml session_options_map_rl_trajectory_controls --lib
• git diff --check