util: zero-pad thread number suffixes

Thread names with numeric suffixes are easier to scan when the suffixes use a fixed width.
Format `ThreadPool` and script-check worker suffixes as two digits while keeping the compact dotted convention.

Co-authored-by: Hodlinator <172445034+hodlinator@users.noreply.github.com>

src/checkqueue.h

@@ -149,7 +149,7 @@ public:
         m_worker_threads.reserve(worker_threads_num);
         for (int n = 0; n < worker_threads_num; ++n) {
             m_worker_threads.emplace_back([this, n]() {
-                util::ThreadRename(strprintf("scriptch.%i", n));
+                util::ThreadRename(strprintf("scriptch.%02i", n));
                 Loop(false /* worker thread */);
             });
         }