perf(discovery): reduce per-file allocations in discovery phase

- Replace QString::split('.') with indexOf/lastIndexOf to extract
  basename and extension without allocating a QList<QString> per file.
- Replace 5 QTimer::singleShot(0,...) calls with
  QMetaObject::invokeMethod(Qt::QueuedConnection) which achieves the
  same deferred invocation without allocating a QTimer on the heap
  each time. In a large sync with many directories, this eliminates
  thousands of unnecessary heap allocations.

Signed-off-by: Qoole <2862661+qoole@users.noreply.github.com>

Author: qoole

src/libsync/discovery.cpp

@@ -250,7 +250,7 @@ void ProcessDirectoryJob::process()
         processFile(std::move(path), e.localEntry, e.serverEntry, e.dbEntry);
     }
     _discoveryData->_listExclusiveFiles.clear();
-    QTimer::singleShot(0, _discoveryData, &DiscoveryPhase::scheduleMoreJobs);
+    QMetaObject::invokeMethod(_discoveryData, &DiscoveryPhase::scheduleMoreJobs, Qt::QueuedConnection);
 }
 
 bool ProcessDirectoryJob::handleExcluded(const QString &path, const Entries &entries, const std::map<QString, Entries> &allEntries, const bool isHidden, const bool isBlacklisted)
@@ -304,9 +304,10 @@ bool ProcessDirectoryJob::handleExcluded(const QString &path, const Entries &ent
     }
 
     const auto &localName = entries.localEntry.name;
-    const auto splitName = localName.split('.');
-    const auto &baseName = splitName.first();
-    const auto extension = splitName.size() > 1 ? splitName.last() : QString();
+    const auto firstDotIndex = localName.indexOf(QLatin1Char('.'));
+    const auto lastDotIndex = localName.lastIndexOf(QLatin1Char('.'));
+    const auto baseName = firstDotIndex >= 0 ? localName.left(firstDotIndex) : localName;
+    const auto extension = lastDotIndex >= 0 ? localName.mid(lastDotIndex + 1) : QString();
     const auto accountCaps = _discoveryData->_account->capabilities();
     const auto forbiddenFilenames = accountCaps.forbiddenFilenames();
     const auto forbiddenBasenames = accountCaps.forbiddenFilenameBasenames();
@@ -699,7 +700,7 @@ void ProcessDirectoryJob::postProcessServerNew(const SyncFileItemPtr &item,
                                                         if (!result) {
                                                             processFileAnalyzeLocalInfo(item, path, localEntry, serverEntry, dbEntry, _queryServer);
                                                         }
-                                                        QTimer::singleShot(0, _discoveryData, &DiscoveryPhase::scheduleMoreJobs);
+                                                        QMetaObject::invokeMethod(_discoveryData, &DiscoveryPhase::scheduleMoreJobs, Qt::QueuedConnection);
                                                     });
         return;
     }
@@ -1063,7 +1064,7 @@ void ProcessDirectoryJob::processFileAnalyzeRemoteInfo(const SyncFileItemPtr &it
             const auto job = new RequestEtagJob(_discoveryData->_account, _discoveryData->_remoteFolder + originalPath, this);
             connect(job, &RequestEtagJob::finishedWithResult, this, [=, this](const HttpResult<QByteArray> &etag) mutable {
                 _pendingAsyncJobs--;
-                QTimer::singleShot(0, _discoveryData, &DiscoveryPhase::scheduleMoreJobs);
+                QMetaObject::invokeMethod(_discoveryData, &DiscoveryPhase::scheduleMoreJobs, Qt::QueuedConnection);
                 if (etag || etag.error().code != 404 ||
                     // Somehow another item claimed this original path, consider as if it existed
                     _discoveryData->isRenamed(originalPath)) {
@@ -1714,7 +1715,7 @@ void ProcessDirectoryJob::processFileAnalyzeLocalInfo(
             }
             processFileFinalize(item, path, item->isDirectory(), NormalQuery, recurseQueryServer);
             _pendingAsyncJobs--;
-            QTimer::singleShot(0, _discoveryData, &DiscoveryPhase::scheduleMoreJobs);
+            QMetaObject::invokeMethod(_discoveryData, &DiscoveryPhase::scheduleMoreJobs, Qt::QueuedConnection);
         });
         job->start();
         return;
@@ -2194,7 +2195,7 @@ void ProcessDirectoryJob::subJobFinished()
     int count = _runningJobs.removeAll(job);
     ASSERT(count == 1);
     job->deleteLater();
-    QTimer::singleShot(0, _discoveryData, &DiscoveryPhase::scheduleMoreJobs);
+    QMetaObject::invokeMethod(_discoveryData, &DiscoveryPhase::scheduleMoreJobs, Qt::QueuedConnection);
 }
 
 int ProcessDirectoryJob::processSubJobs(int nbJobs)