fix: include rollout_path in NewConversationResponse (#3352)

Adding the `rollout_path` to the `NewConversationResponse` makes it so a
client can perform subsequent operations on a `(ConversationId,
PathBuf)` pair. #3353 will introduce support for `ArchiveConversation`.

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[//]: # (BEGIN SAPLING FOOTER)
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* #3353
* __->__ #3352

codex-rs/protocol/Cargo.toml

@@ -28,6 +28,7 @@ uuid = { version = "1", features = ["serde", "v4"] }
 
 [dev-dependencies]
 pretty_assertions = "1.4.1"
+tempfile = "3"
 
 [package.metadata.cargo-shear]
 # Required because the not imported as strum_macros in non-nightly builds.