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>

doc/developer-notes.md

@@ -699,13 +699,13 @@ and its `cs_KeyStore` lock for example).
   : Performs various loading tasks that are part of init but shouldn't block the node from being started: external block import,
    reindex, reindex-chainstate, main chain activation, spawn indexes background sync threads and mempool load.
 
-- [CCheckQueue::Loop (`b-scriptch.x`)](https://doxygen.bitcoincore.org/class_c_check_queue.html#checkqueue)
+- [CCheckQueue::Loop (`b-scriptch.xx`)](https://doxygen.bitcoincore.org/class_c_check_queue.html#checkqueue)
   : Parallel script validation threads for transactions in blocks.
 
 - [ThreadHTTP (`b-http`)](https://doxygen.bitcoincore.org/httpserver_8cpp.html#http)
   : Libevent thread to listen for RPC and REST connections.
 
-- [HTTP worker threads (`b-http.x`)](https://doxygen.bitcoincore.org/httpserver_8cpp.html#http_pool)
+- [HTTP worker threads (`b-http.xx`)](https://doxygen.bitcoincore.org/httpserver_8cpp.html#http_pool)
   : Threads to service RPC and REST requests.
 
 - [Indexer threads (`b-txindex`, etc)](https://doxygen.bitcoincore.org/class_base_index.html#index_sync)

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 */);
             });
         }

src/util/threadpool.h

@@ -112,7 +112,7 @@ public:
         // Create workers
         m_workers.reserve(num_workers);
         for (int i = 0; i < num_workers; i++) {
-            m_workers.emplace_back(&util::TraceThread, strprintf("%s.%d", m_name, i), [this] { WorkerThread(); });
+            m_workers.emplace_back(&util::TraceThread, strprintf("%s.%02d", m_name, i), [this] { WorkerThread(); });
         }
     }