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/protocol/src/mcp_protocol.rs

@@ -19,16 +19,34 @@ use strum_macros::Display;
 use ts_rs::TS;
 use uuid::Uuid;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, TS)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, TS, Hash, Default)]
 #[ts(type = "string")]
 pub struct ConversationId(pub Uuid);
 
+impl ConversationId {
+    pub fn new() -> Self {
+        Self(Uuid::new_v4())
+    }
+}
+
 impl Display for ConversationId {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "{}", self.0)
     }
 }
 
+impl From<Uuid> for ConversationId {
+    fn from(value: Uuid) -> Self {
+        Self(value)
+    }
+}
+
+impl From<ConversationId> for Uuid {
+    fn from(value: ConversationId) -> Self {
+        value.0
+    }
+}
+
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, TS)]
 #[ts(type = "string")]
 pub struct GitSha(pub String);