fix(ci): resolve remaining CI failures

Clippy: Fix 3 unnecessary_sort_by warnings in ringkernel-core by
using sort_by_key(|x| Reverse(x.field)) instead of sort_by closures.
Affected: introspection.rs, scheduling.rs, memory_pressure.rs.

Security Audit: Replace rustsec/audit-check@v2 with direct cargo-audit
invocation. The action was failing with 'Resource not accessible by
integration' due to missing checks:write permission. Our audit showed
zero vulnerabilities — the failure was a permissions/integration issue,
not a security issue.

1485 tests pass, 0 failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mivertowski

.github/workflows/ci.yml

@@ -96,9 +96,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: rustsec/audit-check@v2
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
+      - uses: dtolnay/rust-toolchain@stable
+      - name: Install cargo-audit
+        run: cargo install --locked cargo-audit
+      - name: Run cargo audit
+        # Uses .cargo/audit.toml for ignored advisories (documented transitive deps).
+        # Unmaintained warnings are informational and do not fail the build.
+        run: cargo audit
 
   # Feature matrix: test key feature combinations that work without GPU hardware
   feature-matrix:

crates/ringkernel-core/src/introspection.rs

@@ -135,7 +135,7 @@ impl TraceBuffer {
     /// Get recent trace entries (most recent first).
     pub fn recent(&self, limit: usize) -> Vec<&TraceEntry> {
         let mut result: Vec<&TraceEntry> = self.entries.iter().collect();
-        result.sort_by(|a, b| b.received_at.cmp(&a.received_at));
+        result.sort_by_key(|e| std::cmp::Reverse(e.received_at));
         result.truncate(limit);
         result
     }

crates/ringkernel-core/src/memory_pressure.rs

@@ -236,7 +236,7 @@ impl MemoryPressureMonitor {
             .iter()
             .map(|(&id, b)| (id, b.current_bytes))
             .collect();
-        actors.sort_by(|a, b| b.1.cmp(&a.1));
+        actors.sort_by_key(|a| std::cmp::Reverse(a.1));
         actors
     }
 

crates/ringkernel-core/src/scheduling.rs

@@ -468,7 +468,7 @@ impl LoadTable {
             .collect();
 
         // Sort victims by excess load (descending)
-        victims.sort_by(|a, b| b.1.cmp(&a.1));
+        victims.sort_by_key(|v| std::cmp::Reverse(v.1));
 
         // Match thieves to victims
         let mut victim_idx = 0;