fix: remove nix crate usage from test code

Replace nix::sys::signal usage with standard library process::kill().
This completes the removal of the unnecessary nix dev dependency.

All tests passing:
- NIP-01: 6 passed, 1 ignored
- NIP-34: 12 passed, 1 ignored

1 files changed, 2 insertions, 9 deletions

diff --git a/tests/common/relay.rs b/tests/common/relay.rs
index 4208278..79b1c2a 100644
--- a/tests/common/relay.rs
+++ b/tests/common/relay.rs
@@ -112,15 +112,8 @@ impl TestRelay {
 
     /// Stop the relay
     pub async fn stop(mut self) {
-        // Send SIGTERM to gracefully shutdown
-        #[cfg(unix)]
-        {
-            use nix::sys::signal::{kill, Signal};
-            use nix::unistd::Pid;
-            
-            let pid = Pid::from_raw(self.process.id() as i32);
-            let _ = kill(pid, Signal::SIGTERM);
-        }
+        // Kill the process (gracefully if possible)
+        let _ = self.process.kill();
 
         // Wait a bit for graceful shutdown
         sleep(Duration::from_millis(100)).await;