Why

unix_escalation.rs had a large inline mod tests block that made the implementation harder to scan. This change moves those tests into a sibling file while keeping them as a child module, so they can still exercise private items without widening visibility.

What Changed

• replaced the inline #[cfg(test)] mod tests block in codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs with a path-based test module declaration
• moved the existing unit tests into codex-rs/core/src/tools/runtimes/shell/unix_escalation_tests.rs
• kept the extracted tests using super::... imports so they continue to access private helpers and types from unix_escalation.rs

Testing

• cargo test -p codex-core unix_escalation::tests