Use StringRef for Opt's optNames

Removes another ~70 allocations.

src/catch2/internal/catch_stringref.hpp

@@ -75,7 +75,7 @@ namespace Catch {
         }
 
         // Returns a substring of [start, start + length).
-        // If start + length > size(), then the substring is [start, start + size()).
+        // If start + length > size(), then the substring is [start, size()).
         // If start > size(), then the substring is empty.
         constexpr StringRef substr(size_type start, size_type length) const noexcept {
             if (start < m_size) {