chore: upgrade to Rust 1.92.0 (#8860)

**Summary**
- Upgrade Rust toolchain used by CI to 1.92.0.
- Address new clippy `derivable_impls` warnings by deriving `Default`
for enums across protocol, core, backend openapi models, and
windows-sandbox setup.
- Tidy up related test/config behavior (originator header handling, env
override cleanup) and remove a now-unused assignment in TUI/TUI2 render
layout.

**Testing**
- `just fmt`
- `just fix -p codex-tui`
- `just fix -p codex-tui2`
- `just fix -p codex-windows-sandbox`
- `cargo test -p codex-tui`
- `cargo test -p codex-tui2`
- `cargo test -p codex-windows-sandbox`
- `cargo test -p codex-core --test all`
- `cargo test -p codex-app-server --test all`
- `cargo test -p codex-mcp-server --test all`
- `cargo test --all-features`

codex-rs/codex-backend-openapi-models/src/models/rate_limit_status_payload.rs

@@ -42,9 +42,12 @@ impl RateLimitStatusPayload {
     }
 }
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
+#[derive(
+    Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize, Default,
+)]
 pub enum PlanType {
     #[serde(rename = "guest")]
+    #[default]
     Guest,
     #[serde(rename = "free")]
     Free,
@@ -71,9 +74,3 @@ pub enum PlanType {
     #[serde(rename = "edu")]
     Edu,
 }
-
-impl Default for PlanType {
-    fn default() -> PlanType {
-        Self::Guest
-    }
-}