refactor(app): centralize perf diagnostics and activity coalescing

packages/app/src/runtime/perf-diagnostics/use-perf-diagnostics.ts

@@ -0,0 +1,7 @@
+import { useContext } from "react";
+import { PerfDiagnosticsContext } from "./perf-diagnostics-context";
+import type { PerfDiagnosticsReporter } from "./types";
+
+export function usePerfDiagnostics(): PerfDiagnosticsReporter {
+  return useContext(PerfDiagnosticsContext);
+}