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/core/src/shell.rs

@@ -340,6 +340,7 @@ mod detect_shell_type_tests {
 #[cfg(unix)]
 mod tests {
     use super::*;
+    use std::path::Path;
     use std::path::PathBuf;
     use std::process::Command;
 
@@ -350,7 +351,7 @@ mod tests {
 
         let shell_path = zsh_shell.shell_path;
 
-        assert_eq!(shell_path, PathBuf::from("/bin/zsh"));
+        assert_eq!(shell_path, Path::new("/bin/zsh"));
     }
 
     #[test]
@@ -360,7 +361,7 @@ mod tests {
 
         let shell_path = zsh_shell.shell_path;
 
-        assert_eq!(shell_path, PathBuf::from("/bin/zsh"));
+        assert_eq!(shell_path, Path::new("/bin/zsh"));
     }
 
     #[test]
@@ -369,9 +370,9 @@ mod tests {
         let shell_path = bash_shell.shell_path;
 
         assert!(
-            shell_path == PathBuf::from("/bin/bash")
-                || shell_path == PathBuf::from("/usr/bin/bash")
-                || shell_path == PathBuf::from("/usr/local/bin/bash"),
+            shell_path == Path::new("/bin/bash")
+                || shell_path == Path::new("/usr/bin/bash")
+                || shell_path == Path::new("/usr/local/bin/bash"),
             "shell path: {shell_path:?}",
         );
     }
@@ -381,7 +382,7 @@ mod tests {
         let sh_shell = get_shell(ShellType::Sh, None).unwrap();
         let shell_path = sh_shell.shell_path;
         assert!(
-            shell_path == PathBuf::from("/bin/sh") || shell_path == PathBuf::from("/usr/bin/sh"),
+            shell_path == Path::new("/bin/sh") || shell_path == Path::new("/usr/bin/sh"),
             "shell path: {shell_path:?}",
         );
     }