Fix cache effectiveness test by clearing cache state

- Add Clear() method to Cache struct
- Clear cache at start of TestCacheEffectiveness to ensure fresh state
- Prevents test failures when cache is warmed by previous tests

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: vishr

cookbook/performance/server.go

@@ -44,6 +44,10 @@ func (c *Cache) Set(key string, value any) {
 	c.data[key] = value
 }
 
+func (c *Cache) Clear() {
+	c.data = make(map[string]any)
+}
+
 var cache = NewCache()
 
 // Fast endpoint - minimal processing

cookbook/performance/server_test.go

@@ -135,6 +135,9 @@ func TestResponseTime(t *testing.T) {
 }
 
 func TestCacheEffectiveness(t *testing.T) {
+	// Clear cache to ensure fresh test state
+	cache.Clear()
+
 	e := echo.New()
 	req := httptest.NewRequest(http.MethodGet, "/cached", nil)