Codex tracing and install fixes

[duncankmckinnon]

Summary

• Rework Codex Logfire export around a turn-level chat <model> span reconstructed from the completed turn in the rollout JSONL (with execute_tool children for paired tool calls), replacing per-event tool export for Codex and deduplicating repeated cumulative token-usage reports.
• Add a logfire.json_schema companion attribute when flattening nested/array attributes so Logfire renders gen_ai.input.messages / .output.messages as structured chat content instead of opaque text.
• Add Codex's native hooks.json mechanism (session/subagent/compaction/permission events) alongside the existing notify-based rollout capture, and fix install/uninstall handling for it (including stripping misconfigured Claude hook entries from Codex's config).
• Fix span ordering so a turn's first chat span can't be sorted ahead of the user message that triggered it when the rollout and hook clocks disagree.

Test plan

• pytest (see tests/test_otel_export.py, tests/test_otel_worker.py, tests/test_codex_turn.py, tests/test_codex_hooks_json.py, tests/test_codex_install.py)