Quadruple all HTTP timeouts to prevent timeout errors

- HTTP request timeout: 2s -> 8s
- Stats collection context timeout: 1s -> 4s
- HTTP read header timeout: 10s -> 40s

This should prevent timeout errors when the database is under load
or when complex queries take longer than expected (slow query
threshold is 50ms).

internal/server/server.go

@@ -42,7 +42,7 @@ func (s *Server) Start() error {
 		port = "8080"
 	}
 
-	const readHeaderTimeout = 10 * time.Second
+	const readHeaderTimeout = 40 * time.Second
 	s.srv = &http.Server{
 		Addr:              ":" + port,
 		Handler:           s.router,