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/scripts/setup-windows.ps1

@@ -179,7 +179,7 @@ if (-not (Ensure-Command 'cargo')) {
 Write-Host "==> Configuring Rust toolchain per rust-toolchain.toml" -ForegroundColor Cyan
 
 # Pin to the workspace toolchain and install components
-$toolchain = '1.90.0'
+$toolchain = '1.92.0'
 & rustup toolchain install $toolchain --profile minimal | Out-Host
 & rustup default $toolchain | Out-Host
 & rustup component add clippy rustfmt rust-src --toolchain $toolchain | Out-Host