fix(sandbox): fix macOS lint and older-glibc test linking

Import HashSet only in the Linux-only process scan, and call gettid
through the raw syscall in a test, since the libc wrapper needs glibc
2.30 or newer.

Signed-off-by: Drew Newberry <anewberry@nvidia.com>

Author: drew

crates/openshell-sandbox/src/boundary_io.rs

@@ -7,7 +7,7 @@ use async_trait::async_trait;
 use openshell_isolation_interface::contract::{
     BackendError, BoundaryDuplexStream, BoundaryLoopbackConnector, LoopbackTarget,
 };
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
 use std::sync::atomic::{AtomicU8, Ordering};
 use std::sync::{Arc, Mutex};
 
@@ -371,7 +371,7 @@ fn owned_processes(
     } else {
         roots.to_vec()
     };
-    let mut visited = HashSet::new();
+    let mut visited = std::collections::HashSet::new();
     let mut owned = Vec::new();
     while let Some(pid) = pending.pop() {
         if !visited.insert(pid) {

crates/openshell-sandbox/src/network_broker.rs

@@ -2455,7 +2455,7 @@ mod tests {
                 libc::syscall(
                     libc::SYS_tgkill,
                     libc::getpid(),
-                    libc::gettid(),
+                    libc::syscall(libc::SYS_gettid),
                     libc::SIGCONT,
                 )
             };