Use ConversationId instead of raw Uuids (#3282)

We're trying to migrate from `session_id: Uuid` to `conversation_id:
ConversationId`. Not only does this give us more type safety but it
unifies our terminology across Codex and with the implementation of
session resuming, a conversation (which can span multiple sessions) is
more appropriate.

I started this impl on https://github.com/openai/codex/pull/3219 as part
of getting resume working in the extension but it's big enough that it
should be broken out.

codex-rs/tui/src/history_cell.rs

@@ -27,6 +27,7 @@ use codex_core::protocol::McpInvocation;
 use codex_core::protocol::SandboxPolicy;
 use codex_core::protocol::SessionConfiguredEvent;
 use codex_core::protocol::TokenUsage;
+use codex_protocol::mcp_protocol::ConversationId;
 use codex_protocol::parse_command::ParsedCommand;
 use image::DynamicImage;
 use image::ImageReader;
@@ -49,7 +50,6 @@ use std::time::Duration;
 use std::time::Instant;
 use tracing::error;
 use unicode_width::UnicodeWidthStr;
-use uuid::Uuid;
 
 #[derive(Clone, Debug)]
 pub(crate) struct CommandOutput {
@@ -821,7 +821,7 @@ pub(crate) fn new_completed_mcp_tool_call(
 pub(crate) fn new_status_output(
     config: &Config,
     usage: &TokenUsage,
-    session_id: &Option<Uuid>,
+    session_id: &Option<ConversationId>,
 ) -> PlainHistoryCell {
     let mut lines: Vec<Line<'static>> = Vec::new();
     lines.push("/status".magenta().into());