test(ttlcache): de-flake TestCache_Expiry timing under parallel CI load

The t.Parallel test used TTL=10ms with a 20ms post-TTL sleep, a margin too
tight when the scheduler pauses the goroutine under CI load. Raise the TTL
to 50ms and sleep 5x past it (named const), keeping the test fast (~250ms)
while removing the nondeterminism Copilot flagged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

internal/common/ttlcache/cache_test.go

@@ -84,20 +84,23 @@ func TestCache(t *testing.T) {
 }
 
 // TestCache_Expiry verifies that a cached entry is considered a miss after
-// its TTL has elapsed.  We use a very small TTL and sleep past it.
+// its TTL has elapsed. The TTL is kept small for speed but the post-TTL sleep
+// uses a generous multiple of it so the test stays deterministic under CI load
+// (where this t.Parallel test can be paused between statements).
 func TestCache_Expiry(t *testing.T) {
 	t.Parallel()
+	const ttl = 50 * time.Millisecond
 	var c Cache[int]
-	c.SetTTL(10 * time.Millisecond)
+	c.SetTTL(ttl)
 	c.Set("x", 42)
 
 	// Confirm hit immediately.
 	if _, ok := c.Get("x"); !ok {
 		t.Fatal("Get returned miss immediately after Set; want hit")
 	}
 
-	// Sleep past TTL.
-	time.Sleep(20 * time.Millisecond)
+	// Sleep well past the TTL (5x) to avoid flakiness under scheduler pressure.
+	time.Sleep(5 * ttl)
 
 	if _, ok := c.Get("x"); ok {
 		t.Error("Get returned hit after TTL expired; want miss")