fix: optimization: PVS-Studio warning V801

Redefined the second function argument as a const reference instead of by value to improve performance.

Reported by: PVS-Studio
Signed-off-by: Vyacheslav Ivanov <islavaivanov76@gmail.com>

src/files/files.cpp

@@ -103,7 +103,7 @@ std::string files::read_string(const fs::path& filename) {
     return std::string((const char*)bytes.get(), size);
 }
 
-bool files::write_string(const fs::path& filename, const std::string content) {
+bool files::write_string(const fs::path& filename, const std::string& content) {
     std::ofstream file(filename);
     if (!file) {
         return false;