Remove using namespace std from json_diff.hpp

The directive sat at global scope in a header that DeviceManager.hpp
includes, so most of the GUI compiled with all of std in the global
namespace. 42 files had come to rely on it, mostly for string, vector
and unordered_map, four of them for the ""sv and ""ms literals.

Those sites are qualified. GCodeViewer.cpp spelled the type as
std::vector<::string>, which only resolved through the directive. The
files that use the ""sv and ""ms literals get a file-scope
"using namespace std::string_view_literals;" or
"using namespace std::chrono_literals;", as other sources already do.

AGENTS.md

@@ -4,17 +4,15 @@ OrcaSlicer — open-source C++17 3D slicer. wxWidgets GUI, CMake build system.
 
 ## Build Commands
 
-Build the Release configuration unless asked otherwise.
-
 ```bash
 # macOS
-cmake --build build/arm64 --config Release --target all --
+cmake --build build/arm64 --config RelWithDebInfo --target all --
 
 # Linux
-cmake --build build --config Release --target all --
+cmake --build build --config RelWithDebInfo --target all --
 
-# Windows
+# Windows (replace %build_type% with Debug/Release/RelWithDebInfo)
-cmake --build . --config Release --target ALL_BUILD -- -m
+cmake --build . --config %build_type% --target ALL_BUILD -- -m
 ```
 
 ## Testing

src/slic3r/Utils/OrcaCloudServiceAgent.cpp

@@ -82,7 +82,7 @@ using json = nlohmann::json;
 namespace Slic3r {
 
 namespace {
-constexpr const char* ORCA_DEFAULT_API_URL   = "https://api.orcaslicer.com";
+constexpr const char* ORCA_DEFAULT_API_URL   = "api.orcaslicer.com";
 constexpr const char* ORCA_DEFAULT_AUTH_URL  = "https://auth.orcaslicer.com";
 constexpr const char* ORCA_DEFAULT_CLOUD_URL = "https://cloud.orcaslicer.com";
 // Orca: This is a public key with no secret, used to identify the client application to the backend.