feat: add ArchiveConversation to ClientRequest (#3353)

Adds support for `ArchiveConversation` in the JSON-RPC server that takes
a `(ConversationId, PathBuf)` pair and:

- verifies the `ConversationId` corresponds to the rollout id at the
`PathBuf`
- if so, invokes
`ConversationManager.remove_conversation(ConversationId)`
- if the `CodexConversation` was in memory, send `Shutdown` and wait for
`ShutdownComplete` with a timeout
- moves the `.jsonl` file to `$CODEX_HOME/archived_sessions`

---------

Co-authored-by: Gabriel Peal <gabriel@openai.com>

codex-rs/core/src/lib.rs

@@ -61,7 +61,9 @@ pub mod spawn;
 pub mod terminal;
 mod tool_apply_patch;
 pub mod turn_diff_tracker;
+pub use rollout::ARCHIVED_SESSIONS_SUBDIR;
 pub use rollout::RolloutRecorder;
+pub use rollout::SESSIONS_SUBDIR;
 pub use rollout::SessionMeta;
 pub use rollout::list::ConversationItem;
 pub use rollout::list::ConversationsPage;