Make UUID validation RegEx a static class member

When analyzing a callgrind profile of a full library rescan, I noticed
that there are a lot of CPU instructions coming from libpcre2, with the
call originating in the UUID validation code.

Previously, the regular expression used for UUID validation was parsed
from a string for every invocation of the validation function. This is
unnecessary. A library rescan will validate thousands of UUIDs (roughly
250k calls to `Uuid::isValid` with 200'000 instructions per call on my
laptop for a library rescan). By moving the code to a static class
member, I achieved a 15% speedup for a full library scan.

libs/librepcb/common/uuid.cpp

@@ -30,16 +30,22 @@
  ******************************************************************************/
 namespace librepcb {
 
+/*******************************************************************************
+ *  Static Members
+ ******************************************************************************/
+
+// Initialize validation regex
+const QRegularExpression Uuid::mValidationRe(
+    "\\A[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\\z");
+
 /*******************************************************************************
  *  Static Methods
  ******************************************************************************/
 
 bool Uuid::isValid(const QString& str) noexcept {
   // check format of string (only accept EXACT matches!)
-  QRegularExpression re(
-      "\\A[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\\z");
-  QRegularExpressionMatch match =
-      re.match(str, 0, QRegularExpression::PartialPreferCompleteMatch);
+  QRegularExpressionMatch match = mValidationRe.match(
+      str, 0, QRegularExpression::PartialPreferCompleteMatch);
   if (!match.hasMatch()) return false;
 
   // check type of uuid

libs/librepcb/common/uuid.h

@@ -158,6 +158,11 @@ class Uuid final {
 
 private:          // Data
   QString mUuid;  ///< Guaranteed to always contain a valid UUID
+
+  /**
+   * @brief mRe Regular expression for validating UUIDs.
+   */
+  static const QRegularExpression mValidationRe;
 };
 
 /*******************************************************************************