perf(discovery): use QStringView for forbidden-name checks

Replace QString::split('.') with indexOf/lastIndexOf to extract the
basename and extension without allocating a QList<QString> per file,
and hold the slices as QStringView so the comparisons against
forbiddenFilenames / forbiddenBasenames / forbiddenExtensions run
against zero-copy views into the original QString instead of allocating
new QString copies.

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

Author: qoole

src/libsync/discovery.cpp

@@ -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 ? QStringView(localName).left(firstDotIndex) : QStringView(localName);
+    const auto extension = lastDotIndex >= 0 ? QStringView(localName).mid(lastDotIndex + 1) : QStringView();
     const auto accountCaps = _discoveryData->_account->capabilities();
     const auto forbiddenFilenames = accountCaps.forbiddenFilenames();
     const auto forbiddenBasenames = accountCaps.forbiddenFilenameBasenames();